Optoelectronic Integrated Circuit

ABSTRACT

A semiconductor device employs an epitaxial layer arrangement including a first ohmic contact layer and first modulation doped quantum well structure disposed above the first ohmic contact layer. The first ohmic contact layer has a first doping type, and the first modulation doped quantum well structure has a modulation doped layer of a second doping type. At least one isolation ion implant region is provided that extends through the first ohmic contact layer. The at least one isolation ion implant region can include oxygen ions. The at least one isolation ion implant region can define a region that is substantially free of charge carriers in order to reduce a characteristic capacitance of the device. A variety of high performance transistor devices (e.g., HFET and BICFETs) and optoelectronic devices can employ this device structure. Other aspects of wavelength-tunable microresonantors and related semiconductor fabrication methodologies are also described and claimed.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority from U.S. Prov. Appl. No.61/962,303, filed on Jan. 29, 2014, herein incorporated by reference inits entirety.

BACKGROUND

1. Field

The present application relates to semiconductor integrated circuitsthat implement a variety optoelectronic functions (such as opticalemitters, optical detectors and optical switches) and electronicfunctions (such as heterojunction field effect transistors and bipolarfield effect transistors).

2. State of the Art

The present application builds upon technology (referred to by theApplicant as “Planar Optoelectronic Technology” or “POET”) that providesfor the realization of a variety of devices (optoelectronic devices,logic circuits and/or signal processing circuits) utilizing inversionquantum-well channel device structures as described in detail in U.S.Pat. No. 6,031,243; U.S. patent application Ser. No. 09/556,285, filedon Apr. 24, 2000; U.S. patent application Ser. No. 09/798,316, filed onMar. 2, 2001; International Application No. PCT/US02/06802 filed on Mar.4, 2002; U.S. patent application Ser. No. 08/949,504, filed on Oct. 14,1997, U.S. patent application Ser. No. 10/200,967, filed on Jul. 23,2002; U.S. application Ser. No. 09/710,217, filed on Nov. 10, 2000; U.S.Patent Application No. 60/376,238, filed on Apr. 26, 2002; U.S. patentapplication Ser. No. 10/323,390, filed on Dec. 19, 2002; U.S. patentapplication Ser. No. 10/280,892, filed on Oct. 25, 2002; U.S. patentapplication Ser. No. 10/323,390, filed on Dec. 19, 2002; U.S. patentapplication Ser. No. 10/323,513, filed on Dec. 19, 2002; U.S. patentapplication Ser. No. 10/323,389, filed on Dec. 19, 2002; U.S. patentapplication Ser. No. 10/323,388, filed on Dec. 19, 2002; U.S. patentapplication Ser. No. 10/340,942, filed on Jan. 13, 2003; all of whichare hereby incorporated by reference in their entireties.

With these structures, a fabrication sequence can be used to make thedevices on a common substrate. In other words, n type and p typecontacts, critical etches, etc. can be used to realize all of thesedevices simultaneously on a common substrate. The essential features ofthis device structure include 1) an n-type modulation doped interfaceand a p-type modulation doped quantum well interface, 2) self-alignedn-type and p-type channel contacts formed by ion implantation, 3) n-typemetal contacts to the n-type ion implants and the bottom n-type layerstructure, and 4) p-type metal contacts to the p-type ion implants andthe top p-type layer structure. The active device structures arepreferably realized with a material system of group III-V materials(such as a GaAs/AlGaAs).

POET can be used to construct a variety of optoelectronic devices. POETcan also be used to construct a variety of high performance transistordevices, such as complementary NHFET and PHFET unipolar devices as wellas n-type and p-type HBT bipolar devices.

SUMMARY

A semiconductor device employs an epitaxial layer arrangement includinga first ohmic contact layer and first modulation doped quantum wellstructure disposed above the first ohmic contact layer. The first ohmiccontact layer has a first doping type, and the first modulation dopedquantum well structure has a modulation doped layer of a second dopingtype. At least one isolation ion implant region is provided that extendsthrough the first ohmic contact layer. The at least one isolation ionimplant region can include oxygen ions. The at least one isolation ionimplant region can define a region that is substantially free of chargecarriers in order to reduce a characteristic capacitance of the device.

In one embodiment, the epitaxial layer arrangement further includes atleast one spacer layer disposed above the first modulation doped quantumwell structure. A mesa can be formed in the at least one spacer layer.At least one contact implant region can be disposed below the mesa incontact with the first modulation doped quantum well structure. At leastone electrode terminal can be formed on the mesa in contact with the atleast one contact implant region. The at least one isolation implantregion can be disposed below the mesa and below the at least one contactimplant region.

In another embodiment, the first modulation doped quantum well structuredefines a QW channel of an HFET device, wherein the QW channel extendsbetween opposed contact ion implant regions that are in contact withcorresponding source and drain terminal electrodes of the HFET device,and a gate terminal electrode of the HFET device is in contact with thefirst ohmic contact layer.

In another embodiment, the first modulation doped quantum well structuredefines a QW channel of a BICFET device, wherein the QW channel is incontact with a base terminal electrode of the BICFET device, and anemitter terminal electrode of the BICFET device is in contact with thefirst ohmic contact layer.

In still another embodiment, the at least one isolation implant regionprovides for lateral confinement of light within a resonant cavitydefined by the epitaxial layer arrangement.

In yet another embodiment, the first modulation doped quantum wellstructure, the first ohmic contact layer and the at least one isolationimplant region are all part of an optical resonator formed in theepitaxial layer arrangement, wherein the optical resonator is adapted toprocess light at at least one predetermined wavelength. The opticalresonator can include a resonant cavity supporting propagation of anoptical signal therein, wherein the at least one isolation implant isdisposed adjacent the resonant cavity. A first terminal electrode can beformed in electrical contact with the first modulation doped quantumwell structure. A second terminal electrode can be formed in electricalcontact with the first ohmic contact layer. The first and secondterminal electrodes can be configured as terminals of a diode laserwhereby injected electrical current flows between the first and secondterminal electrodes and causes light generation and propagation withinthe resonant cavity. Alternatively, the first and second terminalelectrodes are configured as terminals of a diode optical detector thatcarry electrical current caused by absorption of light propagatingwithin the resonant cavity.

In another embodiment, the epitaxial layer arrangement can include atleast one spacer layer disposed above the first modulation doped quantumwell structure, a second modulation doped quantum well structuredisposed above the at least one spacer layer, and a second ohmic contactlayer disposed above the second modulation doped quantum well structure.The second modulation doped quantum well structure has a modulationdoped layer of the first doping type, and the second ohmic contact layerhas the second doping type. A top terminal electrode can be formed inelectrical contact with the second ohmic contact layer. A first injectorterminal electrode can be formed in electrical contact with the secondmodulation doped quantum well structure. A second injector terminalelectrode can be formed in electrical contact with the first modulationdoped quantum well structure. A bottom terminal electrode can be formedin electrical contact with the first ohmic contact layer. The topterminal electrode, the first injector terminal electrode, the secondinjector terminal electrode, and the bottom terminal electrode can beconfigured as terminals of a switching thyristor laser having an ONstate whereby current flows between the top terminal electrode andbottom terminal electrode to cause light generation and propagationwithin the resonant cavity. Alternatively, the top terminal electrode,the first injector terminal electrode, the second injector terminalelectrode, and the bottom terminal electrode can be configured asterminals of a switching thyristor optical detector having an ON statewhereby current flows between the top terminal electrode and bottomterminal electrode, wherein the ON state is caused by absorption oflight propagation in the resonant cavity.

In such embodiments, the resonant cavity can have a disk-like shape andthe optical signal comprises a whispering gallery optical signal, or theresonant cavity can have an annular-shape and the optical signalcomprises a circulating optical signal. The at least one isolationimplant region can be disposed adjacent a central region of the resonantcavity or adjacent a peripheral region of the resonant cavity.

In another embodiment, the resonant cavity can be defined by a ribwaveguide, wherein the at least one isolation implant region is disposedon at least one side of the rib waveguide. The rib waveguide can have aplurality of straight sections that are optically coupled together bybend sections. A coupling waveguide structure can be spaced from theresonant cavity of optical resonator to provide for evanescent-waveoptical coupling therebetween.

In one embodiment, the resonant cavity of the optical resonator and thecoupling waveguide structure can be defined by sidewalls of theepitaxial layer arrangement. The epitaxial layer arrangement can bedisposed above a bottom DBR mirror, wherein the sidewalls that definethe resonant cavity of the optical resonator and the coupling waveguidestructure extend downward to the bottom DBR mirror.

In one embodiment, the epitaxial layer arrangement includes an N+ typedoped layer for the first ohmic contact layer, a first plurality oflayers that define a p-type modulation doped quantum well structure forthe first modulation doped quantum well structure, a second plurality oflayers that define an n-type modulation doped quantum well structure forthe second n-type modulation doped structure, and a P+ type doped layerfor the second ohmic contact layer.

In another aspect, a semiconductor device includes a dual-cavity opticalresonator having a first vertical resonant cavity surrounded by a secondannular resonant cavity formed in an epitaxial layer arrangement. Acoupling waveguide structure is spaced from the second resonant cavityof optical resonator to provide for evanescent-wave optical couplingtherebetween. The second resonant cavity of the optical resonator andthe coupling waveguide structure can be defined by sidewalls of theepitaxial layer arrangement. The coupling waveguide structure and theoptical resonator can be configured to perform predetermined modetransformation operations selected from the group consisting of verticalpropagation to in-plane propagation, in-plane propagation to verticalpropagation, wavelength conversion, and combinations thereof.

In one embodiment, the epitaxial layer arrangement includes a firstohmic contact layer, a first modulation doped quantum well structuredisposed above the first ohmic contact layer, at least one spacer layerdisposed above the first modulation doped quantum well structure, asecond modulation doped quantum well structure disposed above the spacerlayer, and a second ohmic contact layer disposed above the secondmodulation doped quantum well structure, wherein the first ohmic contactlayer has a first doping type, the first modulation doped quantum wellstructure has a modulation doped layer of a second doping type, thesecond first modulation doped quantum well structure has a modulationdoped layer of the first doping type, and the second ohmic contact layerhas the second doping type. The dual cavity resonator can include a topterminal electrode in electrical contact with the second ohmic contactlayer, at least one of a first injector terminal electrode s (which isin electrical contact with the second modulation doped quantum wellstructure) and a second injector terminal (which is in electricalcontact with the first modulation doped quantum well structure), and abottom terminal electrode in electrical contact with the first ohmiccontact layer. The electrodes of the device can be configured asterminals of a switching thyristor laser having an ON state wherebycurrent flows between the top terminal electrode and bottom terminalelectrode causes light generation and propagation within the verticalresonant cavity. Alternatively, the electrodes of the device areconfigured as terminals of a switching thyristor optical detector havingan ON state whereby current flows between the top terminal electrode andbottom terminal electrode, wherein the ON state is caused by absorptionof light propagating in the vertical resonant cavity.

In yet another aspect, a semiconductor device includes an opticalresonator including a closed path waveguide that supports circulatingpropagation of light. A waveguide structure is spaced from the closedpath waveguide of the optical resonator to provide for evanescent-waveoptical coupling therebetween. The closed path waveguide includes atleast one active section and a tuning section that is isolated from theat least one active section. The active section is configured togenerate or absorb light that circulates in the closed path waveguide.The tuning section is configured to provide electrical control of thewavelength of the light circulating in the closed path waveguide. Theclosed path waveguide of the optical resonator and the waveguidestructure can both be formed in an epitaxial layer structure thatincludes at least one modulation doped quantum well structure. Thetuning section of the closed path waveguide can include a plurality ofelectrodes for supplying electrical signals that control charge in oneor more quantum wells of the at least one modulation doped quantum wellstructure of the tuning section in order to control the wavelength ofthe light circulating in the closed path waveguide. The tuning sectionof the closed path waveguide can be isolated from the at least oneactive section by passive waveguide sections.

In yet another aspect, a semiconductor device includes an opticalresonator having a closed path waveguide that supports circulatingpropagation of light. A waveguide structure is spaced from the closedpath waveguide of the optical resonator to provide for evanescent-waveoptical coupling therebetween. The waveguide structure has a first enddisposed opposite a second end. A reflector structure is integral to thefirst end of the waveguide structure. The reflector structure includes aBragg-grating that is configured to reflect a particular wavelength oflight. The reflector structure can include two co-planar radio-frequency(RF) traveling wave transmission lines disposed on opposite sides of theBragg-grating along the length of the Bragg-grating. A signal source canbe configured to supply a traveling wave RF signal to the two co-planarRF traveling wave transmission lines in order to selectively vary theparticular wavelength of light that is reflected by the Bragg-grating ofthe reflector structure. The closed path waveguide of the opticalresonator and the waveguide structure and the reflector structure canall be formed in an epitaxial layer structure that includes at least onelayer disposed above a modulation doped quantum well structure, TheBragg-grating can be formed in the at least one layer disposed above themodulation doped quantum well structure.

In yet another aspect, a method is provided for forming a patternedlayer of metal that defines an aperture of an optoelectronic device thatis part of integrated circuit wafer. The method includes depositing andpatterning a first mask on a top surface of the wafer, wherein thepattern of the first mask defines a feature that protects an area of theaperture. An ion implant operation is performed that forms at least oneimplant region adjacent the aperture. Metal is deposited such that themetal covers the top surface and the mask feature. A second mask isdeposited and patterned to define a window that overlies the maskfeature. The window has a smaller width that width of the mask feature.A first etch operation is performed that etches through the windowdefined by the second mask to a depth at or near the top surface. Thefirst etch operation leaves being at least one sidewall of the maskfeature. A second etch operation is performed that etches sideways andundercuts the at least one opposed sidewall of the mask feature as wellas at least one adjacent sidewall of the metal to form the aperture. Thefirst mask can be a dual layer structure of oxide and nitride. Thesecond mask can be a photoresist material. The at least one ion implantregion can provide for current funneling toward an active region underthe aperture and/or lateral confinement of light within the activeregion under the aperture.

In one embodiment, the metal comprises tungsten. The sidewall(s) thatresult from the first etch operation can have a width dimension on theorder of 1-2 μm. The first etch operation can employ an anisotropicetching process that define a near vertical profile for the sidewall(s).The second etch operation can employ a buffer-oxide etchant.

In another aspect, an optoelectronic semiconductor device includes asubstrate and an epitaxial layer arrangement formed on the substrate.The epitaxial layer arrangement includes a buffer structure and anactive device structure formed on the buffer structure. The activedevice structure includes at least one modulation doped quantum wellstructure spaced from a QD-in-QW structure. The buffer structurecomprises a plurality of layer that are configured to accommodatelattice strain due to mismatch between the active device structure andthe substrate.

In one embodiment, the substrate is a GaAs substrate, the at least onemodulation doped quantum well structure includes at least one InGaAsquantum well formed from an alloy of InAs and GaAs that includes atleast 70 percent InAs, and the QD-in-QW structure includes quantum dotsformed from InAs and embedded within at least one InGaAs quantum wellformed from an alloy of InAs and GaAs that includes at least 70 percentInAs. The InGaAs quantum well of the QD-in-QW structure can include atemplate substructure formed below an emission substructure. Thetemplate substructure includes a non-graded InGaAs quantum well formedfrom an alloy of InAs and GaAs that includes less than 70 percent InAs,and the emission substructure includes a graded InGaAs quantum wellformed from an alloy of InAs and GaAs that has a maximum percentage ofInAs of at least 70 percent InAs. The buffer structure can include aplurality of layers formed from an alloy of InAs and AlAs and possibly aperiodic superlattice layer structure comprising a first layer formedfrom an alloy of AlAs and GaAs and a second layer formed from GaAs.

In another aspect, a method of fabricating an optoelectronic devicerealized in an integrated circuit wafer that includes a top layeroverlying a doped ohmic contact layer and semiconductor layerstherebelow. The method includes depositing a protective layer on the toplayer, and depositing and patterning a first mask on the protectivelayer, wherein the pattern of the first mask protects an area for anoptical feature. A first etch operation is performed that etches down tothe doped ohmic contact in order to define the optical feature thatincludes the top layer. The first etch operation exposes the doped ohmiccontact layer on at least one side of the optical feature and leavesbehind at least one sidewall of the optical feature. An ion implantoperation is performed that forms at least one ion implant region in thesemiconductor layers disposed below the exposed doped ohmic contactlayer and adjacent the at least one side of the optical feature. Asecond mask is deposited and patterned to define a window that overliesthe optical feature. A second etch operation is performed that uses thewindow of the second mask to expose the top layer of the opticalfeature.

In one embodiment, the optical feature is selected from group consistingof an aperture, a waveguide layer of an active waveguide structure, anda waveguide layer of a passive waveguide structure.

The method can further include depositing metal such that the metalcovers the optical feature. In this case, the second mask is depositedon the metal and the window defined by the second mask exposes metalthat covers the optical feature, and the second etch operation removesthe metal that covers the optical feature in order to expose the toplayer of the optical feature.

In one embodiment, the optical feature is selected from group consistingof an aperture, a waveguide layer of an active waveguide structure, anda waveguide layer of a passive waveguide structure. The top layer cancomprise an undoped semiconductor layer. The protective layer cancomprise a silicon nitride layer. The first etch operation can employ ananisotropic etching process that define a near vertical profile for theat least one sidewall of the optical feature. The second etch operationcan employ a buffer-oxide etchant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of exemplary layer structures of theoptoelectronic integrated circuit device structures of FIGS. 2A to 9D.

FIGS. 2A-2B illustrate a diode whispering gallery microresonatorrealized as part of an optoelectronic integrated circuit that employsthe layer structure of FIG. 1; FIG. 2A is a schematic top view of thediode whispering gallery microresonator; and FIG. 2B is a schematiccross-sectional view of the diode thyristor whispering gallerymicroresonator along the section labeled 2B-2B of FIG. 2A.

FIG. 3A-3B illustrate a diode ring microresonator realized as part of anoptoelectronic integrated circuit that employs the layer structure ofFIG. 1; FIG. 3A is a schematic top view of the diode ringmicroresonator; and FIG. 3B is a schematic cross-sectional view of thediode ring microresonator along the section labeled 3B-3B of FIG. 3A.

FIGS. 4A-4B illustrate a thyristor whispering gallery microresonatorrealized as part of an optoelectronic integrated circuit that employsthe layer structure of FIG. 1; FIG. 4A is a schematic top view of thethyristor whispering gallery microresonator; and FIG. 4B is a schematiccross-sectional view of the thyristor whispering gallery microresonatoralong the section labeled 4B-4B of FIG. 4A.

FIGS. 5A-5E illustrates an embodiment of a closed-loop (rectangularpath) microresonator realized as part of an optoelectronic integratedcircuit that employs the layer structure of FIG. 1; FIG. 5A is aschematic top view of the closed-loop microresonator; FIG. 5B is aschematic cross-sectional view of the closed-loop microresonator alongthe section labeled 5B-5B of FIG. 5A; FIG. 5C is a schematiccross-sectional view of the closed-loop microresonator along the sectionlabeled 5C-5C of FIG. 5A; FIG. 5D is a schematic cross-sectional view ofthe closed-loop microresonator along the section labeled 5D-5D of FIG.5A; and FIG. 5E is a schematic cross-sectional view of the closed-loopmicroresonator along the section labeled 5E-5E of FIG. 5A.

FIGS. 5F-5H illustrates an embodiment of a closed-loop (rectangularpath) microresonator and electrically-controlled tuning reflector thatare realized as part of an optoelectronic integrated circuit thatemploys the layer structure of FIG. 1; FIG. 5F is a schematic top viewof the closed-loop microresonator and electrically-controlled tuningreflector; FIG. 5G is a schematic cross-sectional view of the tuningreflector along the section labeled 5G-5GB of FIG. 5F; and FIG. 5H is across-section through the tuning reflector along the section labeled5H-5H of FIG. 5F.

FIGS. 6A-6C illustrate an embodiment of a split-electrode verticalcavity surface emitting device realized as part of an optoelectronicintegrated circuit that employs the layer structure of FIG. 1; FIG. 6Ais a schematic top view of the split-electrode vertical cavity surfaceemitting device; FIG. 6B is a schematic cross-sectional view of thesplit-electrode vertical cavity surface emitting device along thesection labeled 6B-6B of FIG. 6A; and FIG. 6C is a schematiccross-sectional view of the split-electrode vertical cavity surfaceemitting device along the section labeled 6C-6C of FIG. 6A.

FIGS. 7A to 7C illustrate an embodiment of a p-channel HFET devicerealized as part of an optoelectronic integrated circuit that employsthe layer structure of FIG. 1; FIG. 7A is a schematic top view of thep-channel HFET device; FIG. 7B is a schematic cross-sectional view ofthe p-channel HFET device along the section labeled 7B-7B of FIG. 7A;and FIG. 7C is a schematic cross-sectional view of the p-channel HFETdevice along the section labeled 7C-7C of FIG. 7A.

FIGS. 8A to 8C illustrates a dual-wavelength hybrid device realized aspart of an optoelectronic integrated circuit that employs the layerstructure of FIG. 1; FIG. 8A is a schematic top view of thedual-wavelength hybrid device; FIG. 8B is a schematic cross-sectionalview of the dual-wavelength hybrid device along the section labeled8B-8B of FIG. 8A; and FIG. 8C is a schematic cross-sectional view of thedual-wavelength hybrid device along the section labeled 8C-8C of FIG.8A.

FIGS. 9A to 9D illustrate exemplary fabrication steps that form dopantimplant regions that are self-aligned to patterned metal as part of anoptoelectronic device realized in an integrated circuit wafer thatemploys the layer structure of FIG. 1.

FIG. 10 is a schematic illustration of another exemplary layer structurefor realizing the optoelectronic integrated circuit device structuresdescribed herein.

FIGS. 11A to 11F, collectively, are a chart illustrating an exemplarylayer structure for realizing the optoelectronic integrated circuitdevice structures described herein.

FIGS. 12A to 12I illustrate exemplary fabrication steps that form anaperture (or in-plane waveguide) in conjunction with patterned metalelectrodes and/or aligned implant regions as part of an optoelectronicdevice realized in an integrated circuit that employs the layerstructure of FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to FIG. 1, the device structure of the present applicationincludes a bottom dielectric distributed Bragg reflector (DBR) mirror 12formed on substrate 10. The bottom DBR mirror 12 is typically formed bydepositing pairs of semiconductor or dielectric materials with differentrefractive indices. When two materials with different refractive indicesare placed together to form a junction, light will be reflected at thejunction. The amount of light reflected at one such boundary is small.However, if multiple junctions/layer pairs are stacked periodically witheach layer having a quarter-wave (λ/4) optical thickness, thereflections from each of the boundaries will be added in phase toproduce a large amount of reflected light (e.g., a large reflectioncoefficient) at the particular center wavelength λ_(C). Deposited uponthe bottom DBR mirror 12 is the active device structure suitable forrealizing complementary heterostructure field-effect transistor (HFET)devices. The first of these complementary HFET devices is a p-channelHFET which has a p-type modulation doped quantum well (QW) structure 20with an n-type gate region (i.e., n-type ohmic contact layer 14 andn-type layer(s) 16)) below the p-type modulation doped QW structure 20.An undoped spacer layer 18 is disposed between the p-type modulationdoped quantum well (QW) structure 20 and the underlying n-type layer(s)16. One or more spacer layers 22 are disposed above the p-typemodulation doped QW structure 20. The spacer layers 22 can include afirst QD-In-QW structure (not shown) formed above the p-type modulationdoped QW structure 20, where the first QD-In-QW structure includes atleast one QW layer with self-assembled quantum dots (QDs) embeddedtherein. The first QD-In-QW structure can be spaced from the QW(s) ofthe p-type modulation doped QW structure 20 by an undoped spacer layertherebetween. The second of these complementary HFET devices is ann-channel HFET which includes an n-type modulation doped QW structure 24with a p-type gate region (i.e., p-type layer(s) 28 and p-type ohmiccontact 30) formed above the n-type modulation doped QW structure 24. Anundoped spacer layer 26 is disposed between the n-type modulation dopedquantum well (QW) structure 24 and the overlying p-type layer(s) 28. Thespacer layers 22 can also include a second QD-In-QW structure (notshown) formed below the n-type modulation doped QW structure 24, wherethe second QD-In-QW structure includes at least one QW layer withself-assembled quantum dots (QDs) embedded therein. The second QD-In-QWstructure can be spaced from the QW(s) of the n-type modulation doped QWstructure 24 by an undoped spacer layer therebetween. The layersencompassing the spacer layer 22 and the n-type modulation doped QWstructure 24 forms the collector region of the p-channel HFET.Similarly, the layers encompassing the spacer layer 22 and the p-typemodulation doped QW structure 20 forms the collector region of then-channel HFET. Such collector regions are analogous to the substrateregion of a MOSFET device as is well known. Therefore a non-invertedn-channel HFET device is stacked upon an inverted p-channel HFET deviceas part of the active device structure.

The active device layer structure begins with n-type ohmic contactlayer(s) 14 which enables the formation of ohmic contacts thereto.Deposited on layer 14 are one or more n-type layers 16 and an undopedspacer layer 18 which serve electrically as part of the gate of thep-channel HFET device and optically as a part of the lower waveguidecladding of the device. Deposited on layer 18 is the p-type modulationdoped QW structure 20 that defines a p-type charge sheet offset from oneor more QWs (which may be formed from strained or unstrainedheterojunction materials) by an undoped spacer layer. The p-type chargesheet is formed first below the undoped spacer and the one or more QWsof the p-type modulation doped QW structure 20. All of the layers grownthus far form the p-channel HFET device with the gate ohmic contact onthe bottom. Deposited on the p-type modulation doped QW structure 20 isone or more spacer layers 22. The spacer layers 22 can include first andQD-In-QW structures (not shown) that correspond to the p-type modulationdoped QW structure 20 and the n-type modulation doped QW structure 24,respectively, and are offset from the corresponding structure by arespective undoped spacer layer.

Deposited on the spacer layer(s) 22 is the n-type modulation doped QWstructure 24. The n-type modulation doped QW structure 24 defines ann-type charge sheet offset from one or more QWs by an undoped spacerlayer. The n-type charge sheet is formed last above the undoped spacerand the one or more QWs of the n-type modulation doped QW structure 24.

Deposited on the n-type modulation doped QW structure 24 is an undopedspacer layer 26 and one or more p-type layers 28 which can serveelectrically as part of the gate of the n-channel HFET and optically aspart of the upper waveguide cladding of the device. Preferably, thep-type layers 28 include two sheets of planar doping of highly dopedp-material separated by a lightly doped layer of p-material. Thesep-type layers are offset from the n-type modulation doped quantum wellstructure 24 by the undoped spacer layer 26. In this configuration, thetop charge sheet achieves low gate contact resistance and the bottomcharge sheet defines the capacitance of the n-channel HFET with respectto the n-type modulation doped QW structure 24. Deposited on p-typelayer(s) 28 is one or more p-type ohmic contact layer(s) 30, whichenables the formation of ohmic contacts thereto.

For the n-channel HFET device, a gate terminal electrode (not shown) ofthe n-channel HFET device is operably coupled to the top p-type ohmiccontact layer(s) 30. A source terminal electrode (not shown) and a drainterminal electrode (not shown) of the n-channel HFET device are operablycoupled to opposite ends of a QW channel(s) realized in the n-typemodulation doped QW structure 24. One or more terminal electrodes (notshown) can be operably coupled to the p-type modulation doped QWstructure 20 and used as collector terminal electrodes for the n-channelHFET device.

An exemplary embodiment of the p-channel HFET device is shown in FIGS.7A-7C, which includes a gate terminal electrode (G), a source terminalelectrode (S), a drain terminal electrode (D), and a collector terminalelectrode (Coll). The source terminal electrode (S) and the drainterminal electrode (D) are operably coupled to opposite sides of anelongate QW channel(s) realized in the p-type modulation doped QWstructure 20. The layer structure of the p-channel HFET device ispatterned and etched down to spacer layer 22 to form a top mesa 711 atspacer layer 22 for the collector electrode (Coll).

The resulting structure is then patterned and etched to form opposedelongate mesas 713, 715 in the spacer layer 22 above the p-typemodulation doped QW structure 20. The elongate mesas 713, 715 aredisposed on opposite sides of the elongate collector terminal electrode(Coll) along the lengthwise dimension of the collector terminalelectrode (Coll) as best shown in FIGS. 7A and 7B.

A sequence of two different ion implant operations is then carried outto implant ions through the elongate mesas 713, 715. The first implantoperation employs p-type acceptor ions, such as beryllium ions, to formp-type ion implant regions 719 that create the self-aligned p-typecontacts to the p-type modulation doped quantum well structure 20 thatforms the QW channel of the p-channel HFET device. This implant can alsopossibly be accompanied by an implant of fluorine ions to prevent upwarddiffusion. A rapid thermal anneal (RTA) oxide is then deposited on theresultant structure and RTA operations are carried (for example, at 850°C. for 10 seconds) to activate the implant regions 719. After the RTA iscomplete, a second implant operation is carried out involving oxygenions to form high resistance deep oxygen ion implant regions 721 in thebottom n+ contact layer 14, where such high resistance effectivelyblocks current flow therethrough. The peak density of the oxygen ionimplant regions 721 can be controlled to provide the desired resistance.In one embodiment, the peak density of the oxygen ion implant regions721 is at or near 1e¹⁹ cm-3. Multiple implants of oxygen ions atdifferent energies can be used to provide complete coverage of thethickness of the bottom n+ contact layer 14. An RTA is then performed(preferably at 500° C. for about 15 seconds) in order to activate theoxygen ion implant regions 721. Note that the implant regions 719 and721 are stacked on top another under both the source mesa 713 and thedrain mesa 715 as best shown in FIG. 7B and extend parallel to the QWchannel under the collector terminal electrode (Coll) along thelengthwise dimension of the QW channel on opposite sides of the QWchannel. The current blocking oxygen ion implant regions 721 define anisolation region between the p-type implant regions 719 and the bottomN+-type ohmic contact layer 14 of the layer structure. Such isolationregion is substantially devoid of conducting species and significantlyreduces the capacitance between the source terminal electrode (S) andthe gate terminal electrode (G). This capacitance can drastically lowerthe speed of response of the PHFET device if not reduced. Note thetemperature (e.g., 500° C.) of the rapid thermal anneal operation thatactivates the oxygen ions of the implant regions 721 can besignificantly less than the temperature (e.g., 850° C.) of the rapidthermal anneal operation that activates the ions of the implant regions719.

The resulting structure is then etched to form a mesa 723 at the bottomn-type ohmic contact layer(s) 14 for the gate terminal electrode (G) asbest shown in FIG. 7C.

The metal that defines the elongate collector terminal electrode (Coll),which is preferably a W—In alloy, is deposited and patterned on the topmesa 711 above the elongate QW channel in contact with the spacer layer22. The metal of the collector terminal electrode (Coll) can have a widetab-region 709 offset laterally from the source and drain terminalelectrodes as best shown in FIG. 7A. The metal of the source and drainterminal electrodes (S) and (D), which is preferably an Au—Be alloy, isdeposited and patterned on the mesas 713 and 715 in contact with thep-type ion implant regions 719 in order to contact the p-type modulationdoped QW structure 20 that forms the QW channel of the p-channel deviceas best shown in FIG. 7B. The metal of the gate terminal electrode (G),which is preferably an Au—Ge—Ni alloy, is deposited and patterned on themesa 723 in contact with the bottom n-type ohmic contact layer(s) 14 asbest shown in FIG. 7C. The resultant structure can be heated to treatthe metal alloys of the source, drain and gate electrodes as desired. Inone embodiment, the resultant structure can be heated at 420° C. totreat the metal alloys of the source, drain, gate and collectorelectrodes of the device.

Both the n-channel HFET device and the p-channel HFET device are fieldeffect transistors where current flows as a two-dimensional gas througha QW channel with contacts at either end. The basic transistor action isthe modulation of the QW channel conductance by a modulated electricfield that is perpendicular to the QW channel. The modulated electricfield modulates the QW channel conductance by controlling an inversionlayer (i.e., a two-dimensional electron gas for the n-channel HFETdevice or a two-dimensional hole gas for the p-channel HFET) as afunction of gate voltage relative to source voltage.

For the n-channel HFET device, the QW channel conductance is turned onby biasing the gate terminal electrode and the source terminal electrodeat voltages where the P/N junction of the gate and source regions isforward biased with minimal gate conduction and an inversion layer ofelectron gas is created in the QW channel of the n-type modulation dopedquantum well structure 24 between the source terminal electrode and thedrain terminal electrode. In this configuration, the source terminalelectrode is the terminal electrode from which the electron carriersenter the QW channel of the n-type modulation doped quantum wellstructure 24, the drain terminal electrode is the terminal electrodewhere the electron carriers leave the device, and the gate terminalelectrode is the control terminal for the device.

The p-channel HFET device of FIGS. 7A-7C operates in a similar manner tothe n-channel HFET device with the current direction and voltagepolarities reversed with respect to those of the n-channel HFET device.For the p-channel HFET device, the QW channel conductance is turned onby biasing the gate terminal electrode (G) and the source terminalelectrode (S) at a voltage where the P/N junction of the source and gateregions is forward-biased with minimal gate conduction and an inversionlayer of hole gas is created in the QW channel of the p-type modulationdoped quantum well structure 20 between the source terminal electrode(S) and the drain terminal electrode (S). In this configuration, thesource terminal electrode (S) is the terminal from which the holecarriers enter the QW channel of the p-type modulation doped quantumwell structure 20, the drain terminal electrode (D) is the terminalwhere the hole carriers leave the device, and the gate terminalelectrode (G) is the control terminal for the device.

The device structure of the present application can also be configuredto realize bipolar inversion channel field-effect transistors (BICFETs)with either an n-type modulation doped quantum well inversion channelbase region (n-channel base BICFET) or a p-type modulation doped quantumwell inversion channel base region (p-channel base BICFET).

For the n-channel base BICFET device, an emitter terminal electrode (notshown) of the n-channel base BICFET device is operably coupled to thetop p-type ohmic contact layer(s) 30 of the active device structure. Abase terminal electrode (not shown) of the n-channel base BICFET deviceis operably coupled to the QW channel(s) realized in the n-typemodulation doped QW structure 24. A collector terminal electrode (notshown) of the n-channel base BICFET device is operably coupled to thep-type modulation doped QW structure 20. The n-channel base BICFETdevice is a bipolar junction type transistor which can be operated in anactive mode by applying a forward bias to the PN junction of the emitterand base regions while applying a reverse bias to the PN junction of thebase and collector regions, which causes holes to be injected from theemitter terminal electrode to the collector terminal electrode. Becausethe holes are positive carriers, their injection contributes to currentflowing out of the collector terminal electrode as well as currentflowing into the emitter terminal electrode. The bias conditions alsocause electrons to be injected from the base to the emitter, whichcontributes to current flowing out of the base terminal electrode aswell as the current flowing into the emitter terminal electrode.

The p-channel base BICFET device is similar in construction to thep-channel HFET device of FIGS. 7A-7C with the following adaptations. Anemitter terminal electrode of the p-channel base BICFET device, which isanalogous to the gate terminal electrode of the p-channel HFET device,is operably coupled to the bottom n-type ohmic contact layer(s) 14 ofthe active device structure. A base terminal electrode of the p-channelbase BICFET device, which is analogous to the source or drain electrodeof the p-channel HFET device, is operably coupled to the QW channel(s)realized in the p-type modulation doped QW structure 20. A collectorterminal electrode of the p-channel base BICFET device, which isanalogous to the collector terminal electrode of the p-channel HFETdevice, is operably coupled to the spacer layer 22. The p-channel baseBICFET device is a bipolar junction type transistor which can beoperated in an active mode by applying a forward bias to the PN junctionof the emitter and base regions while applying a reverse bias to the PNjunction of the base and collector regions, which causes electrons to beinjected from the emitter terminal electrode to the collector terminalelectrode. Because the electrons are negative carriers, their injectioncontributes to current flowing into the collector terminal electrode aswell as current flowing out of the emitter terminal electrode. The biasconditions also cause holes to be injected from the base to the emitter,which contributes to current flowing into the base terminal electrode aswell as the current flowing out of the emitter terminal electrode.

The device structure of the present application can also be configuredto realize optoelectronic devices such as an electrically-pumped laseror optical detector. To form a resonant cavity device for optical signalemission and/or detection, a top mirror can be formed over the activedevice structure described above. The top mirror can be formed bydepositing pairs of semiconductor or dielectric materials with differentrefractive indices.

In one configuration, the resonant cavity of the device can beconfigured as a vertical cavity and light may enter and exit thevertical cavity through an optical aperture (not shown) in the topsurface of the device such that the device operates as a vertical cavitysurface emitting laser/detector. In this configuration, the distancebetween the top mirror and the bottom DBR mirror 12 represents thelength of the optical cavity and can be set to correspond to thedesignated wavelength (such as 1 to 3 times the designated wavelength).This distance can take into account the penetration depth of the lightinto the bottom and top mirror. This distance is controlled by adjustingthe thickness of one or more of the layers therebetween to enable thiscondition.

In another configuration, the resonant cavity of the device can beconfigured as a whispering gallery or closed-loop microresonator tosupport propagation of an optical mode signal within a waveguide regionformed from the device structure. For the whispering gallerymicroresonator, the waveguide region can be a disk-like structure thatsupports propagation of a whispering gallery mode. The geometry of thedisk-like structure is tuned to the particular wavelength of thewhispering gallery mode. For example, the circumference of the disk-likestructure can be configured to correspond to an integral number ofwavelengths of a standing wave that circulates in the disk-likestructure. For relatively small disk-like structures (e.g., 10 μm indiameter or less), the free spectral range FSR is large enough such thatthe diameter of the disk-like structure can dictate the particularwavelength of the whispering gallery mode. For the closed-loopmicroresonator, the waveguide can support circulating propagation of anoptical mode that follows a circular optical path, a rectangular opticalpath, an oval optical path, or other suitable geometry. The optical pathlength of the closed-loop waveguide is tuned to the particularwavelength of the optical mode signal that is to propagate in theclosed-loop waveguide. At least one coupling waveguide is formedintegral to and adjacent the whispering gallery or closed-loopmicroresonator. The coupling waveguide provides for evanescent couplingof light to and/or from the whispering gallery or closed-loopmicroresonator. Specifically, for the laser, the whispering gallery modeproduced by the whispering gallery microresonator or the optical modesignal that circulates in the closed-loop waveguide of the closed-loopmicroresonator is coupled to the coupling waveguide to produce an outputoptical signal that propagates in the coupling waveguide for outputtherefrom. For the detector, an input optical light is supplied to thecoupling waveguide, which couples the input optical light as awhispering gallery mode in the whispering gallery microresonator fordetection or as an optical mode signal that circulates in theclosed-loop waveguide of the closed-loop microresonator for detection.

In the vertical cavity surface emitting laser/detector as well as thewhispering gallery or closed-loop microresonator, an anode terminalelectrode can be operably coupled to the top p-type ohmic contactlayer(s) 30, and a cathode terminal electrode can be operably coupled tothe n-type modulation doped QW structure 24. One or more optionalelectrodes can be operably coupled to the p-type modulation doped QWstructure 20 as well as to the bottom n-type ohmic contact layer(s) 14.If present, these optional electrodes are configured to floatelectrically with respect to the electrical signals of the anodeterminal electrode as well as of the cathode terminal electrode. In thismanner, the p-type region of the p-type modulation doped QW structure 20floats with respect to the electrical signals of the anode terminalelectrode as well as of the cathode terminal electrode. Electrically,this configuration operates as an electrically-pumped diode laser ordiode detector. This configuration is referred to herein as the topdiode laser or top diode detector because the anode terminal electrodeis operably coupled to the top p-type ohmic contact layer(s) 30 and thecathode terminal electrode is operably coupled to the n-type modulationdoped QW structure 24.

For the top diode laser, the anode terminal electrode is forward biasedrelative to the cathode terminal electrode such that holes are injectedfrom the anode terminal electrode into the QW channel(s) realized in then-type modulation doped QW structure 24 in order to induce photonemission within the device structure. The lower p-type region of theactive device structure (which includes the p-type modulation doped QWstructure 20) floats with respect to the electrical signals of the anodeterminal electrode as well as of the cathode terminal electrode. For thevertical cavity surface emitting laser, the photon emission within thedevice structure produces the optical mode that is emitted verticallythrough the top surface of the device structure. For the whisperinggallery microresonator, the photon emission within the device structureproduces the whispering gallery mode signal that circulates in thewaveguide of the whispering gallery microresonator. For the closed-loopmicroresonator, the photon emission within the device structure producesthe optical mode signal that circulates in the closed-loop waveguide ofthe closed-loop microresonator. In all of these configurations, the topdiode laser operates by injecting electrons into the QW channel of then-type modulation doped QW structure 24, which lowers the barrier of then-type modulation doped QW structure 24 and allows holes to flow overthis barrier to the QW of the p-type modulation doped QW structure 20.In passing over the barrier, very few holes are captured in the QW ofthe n-type modulation doped QW structure 24. Simultaneously, holesdiffuse upwards from the QW of the p-type modulation doped QW structure20 to the QW of the n-type modulation doped QW structure 24 where theyrecombine with the injected electrons to produce stimulated emission.However, it is also noted that the same process of diffusion of holesfrom the lower p-type modulation doped QW structure 20 to the uppern-type modulation doped QW structure 24 also applies to the electronsinjected into the n-type modulation doped QW structure 24. In this way,the n-type modulation doped QW structure 24 supplies electrons bydiffusion to the p-type modulation doped QW structure 20. That meansthere will also be electrons and holes in the lower p-type modulationdoped QW structure 20 and therefore recombination and stimulatedemission. This means that the lower p-type modulation doped QW structure20 is not a loss mechanism but instead can contribute to the laseroutput even though there is no electrical contact to the lower QWstructure. The laser contribution of the lower p-type modulation dopedQW structure 20 may be somewhat less than the upper n-type modulationdoped QW structure 24. It is also noted that in order for this processto work, the lower p-type modulation doped QW structure 20 must beallowed to float in potential so to allow the carrier diffusionmechanisms to operate as described above.

For the top diode detector, the anode terminal electrode is reversedbiased relative to the cathode terminal electrode. The lower p-typeregion of the active device structure (which includes the p-typemodulation doped QW structure 20) floats with respect to the electricalsignals of the anode terminal electrode as well as of the cathodeterminal electrode. The reverse bias conditions are selected such thatthe device produces photocurrent proportional to the intensity of anoptical signal absorbed by the device structure. For the vertical cavitysurface detector, the device structure absorbs the optical mode that isreceived vertically through the top surface of the device structure. Forthe whispering gallery microresonator, the device structure absorbs thewhispering gallery mode that propagates in the waveguide of thewhispering gallery microresonator. For the closed-loop microresonator,the device structure absorbs the optical mode signal that circulates inthe closed-loop waveguide of the closed-loop microresonator.

In the vertical cavity surface emitting laser/detector as well as thewhispering gallery and closed-loop microresonator, an anode terminalelectrode can be operably coupled to the p-type modulation doped QWstructure 20, and a cathode terminal electrode can be operably coupledto the bottom n-type ohmic contact layer(s) 14. One or more optionalelectrodes can be operably coupled to the n-type modulation doped QWstructure 24 as well as to the top p-type ohmic contact layer(s) 30. Ifpresent, these optional electrodes are configured to float electricallywith respect to the electrical signals of the anode terminal electrodeas well as of the cathode terminal electrode. In this manner, the n-typeregion of the n-type modulation doped QW structure 24 floats withrespect to the electrical signals of the anode terminal electrode aswell as of the cathode terminal electrode. Electrically, thisconfiguration operates as an electrically-pumped diode laser or diodedetector. This configuration is referred to herein as the bottom diodelaser or bottom diode detector because the anode terminal electrode isoperably coupled to the p-type modulation doped QW structure 20, and acathode terminal electrode is operably coupled to the bottom n-typeohmic contact layer(s) 14.

For the bottom diode laser, the anode terminal electrode is forwardedbiased relative to the cathode terminal electrode such that holes areinjected from the anode terminal electrode into the QW channel(s)realized in the p-type modulation doped QW structure 20 in order toinduce photon emission within the device structure. The n-type region ofthe n-type modulation doped QW structure 24, when present, floats withrespect to the electrical signals of the anode terminal electrode aswell as of the cathode terminal electrode. For the vertical cavitysurface emitting laser, the photon emission within the device structureproduces the optical mode that is emitted vertically through the topsurface of the device structure. For the whispering gallerymicroresonator, the photon emission within the device structure producesthe whispering gallery mode that circulates in the waveguide of thewhispering gallery microresonator. For the closed-loop microresonator,the photon emission within the device structure produces the opticalmode signal that circulates in the closed-loop waveguide of theclosed-loop microresonator. In all these configurations, the bottomdiode laser operates by injecting holes into the QW channel of thep-type modulation doped QW structure 20. For the case where the n-typemodulation doped QW structure 24 is present (i.e., it has not beenetched away, for example as described with reference to the device ofFIGS. 2A and 2B), the upper n-type modulation doped QW structure 24 cancontribute to emission. It is also noted that in order for this processto work, the upper n-type modulation doped QW structure 24 must beallowed to float in potential so to allow carrier diffusion mechanismsthat stimulate such emission to operate.

For the bottom diode detector, the anode terminal electrode is reversedbiased relative to the cathode terminal electrode. The n-type region ofthe modulation doped QW structure 24 floats with respect to theelectrical signals of the anode terminal electrode as well as of thecathode terminal electrode. The reverse bias conditions are selectedsuch that the device produces photocurrent proportional to the intensityof an optical signal absorbed by the device structure. For the verticalcavity surface detector, the device structure absorbs the optical modethat is received vertically through the top surface of the devicestructure. For the whispering gallery microresonator, the devicestructure absorbs the whispering gallery mode that circulates in thewaveguide region of the whispering gallery microresonator. For theclosed-loop microresonator, the device structure absorbs the opticalmode signal that circulates in the closed-loop waveguide of theclosed-loop microresonator.

In the vertical cavity surface emitting laser/detector as well as thewhispering gallery and closed-loop microresonators, at least one anodeterminal electrode can be operably coupled to the top p-type contactlayer 30, a bottom cathode terminal electrode can be operably coupled tothe bottom n-type contact layer 14, an n-channel injector terminal canbe operably coupled to the n-type modulation doped QW structure 24. Ap-channel injector terminal can also be operably coupled to the p-typemodulation doped QW structure 20. Electrically, this configurationoperates as an electrically-pumped thyristor laser or thyristordetector.

For the thyristor laser, the device structure switches from anon-conducting/OFF state (where the current I through the device issubstantially zero) to a conducting/ON state (where current I ssubstantially greater than zero) when i) the anode terminal electrode isforward biased with respect to the cathode terminal electrode and ii)the voltage between n-channel injector and the anode electrode is biasedsuch that charge is produced in the n-type modulation doped QW structure32 that is greater than the critical switching charge Q_(CR), which isthat charge that reduces the forward breakdown voltage such that no offstate bias point exists. The voltage between p-channel injectorelectrode and cathode electrode can also be configured to produce acharge in the p-type modulation doped QW structure 20 that is greaterthan the critical switching charge Q_(CR). The critical switching chargeQ_(CR) is unique to the geometries and doping levels of the device. Thedevice switches from the conducting/ON state (where the current I issubstantially greater than zero) to a non-conducting/OFF state (wherecurrent I is substantially zero) when the current I through device fallsbelow the hold current of the device for a sufficient period of timesuch that the charge in the n-type modulation doped QW structure 24 (orthe charge in the p-type modulation doped QW structure 20) decreasesbelow the holding charge Q_(H), which is the critical value of thechannel charge which will sustain holding action. Thus, if the anodeterminal is forward biased with respect to the cathode terminal and then-channel injector terminal (and/or the p-channel injector terminal) isbiased to produce the critical switching charge Q_(CR) in the n-typemodulation doped QW structure 24 (or in the p-type modulation doped QWstructure 20), then the device will switch to its conducting/ON state.If the current I in the conducting/ON state is above the threshold forlasing I_(TH), then photon emission will occur within the devicestructure. For the vertical cavity surface emitting laser, the photonemission within the device structure produces the optical mode that isemitted vertically through the top surface of the device structure. Forthe whispering gallery microresonator, the photon emission within thedevice structure produces the whispering gallery mode signal thatcirculates in the waveguide region of the whispering gallerymicroresonator. For the closed-loop microresonator, the photon emissionwithin the device structure produces the optical mode signal thatcirculates in the closed-loop waveguide of the closed-loopmicroresonator.

For the thyristor detector, the device structure switches from anon-conducting/OFF state (where the current I through the device issubstantially zero) to a conducting/ON state (where current I issubstantially greater than zero) in response to an input optical signalthat produces charge in the n-type modulation doped QW structure 24and/or the p-type modulation doped QW structure 20 resulting from photonabsorption of the input optical signal. Specifically, the anode terminalelectrode is forward biased with respect to the cathode terminalelectrode and the voltage between n-channel injector and the anodeelectrode (and/or the voltage between the p-channel injector and thecathode terminal electrode) is biased such that that charged produced inthe n-type modulation doped QW structure 24 (and/or the p-typemodulation doped QW structure 20) resulting from photon absorption ofthe input optical pulse is greater than the critical switching chargeQ_(CR). When the input optical signal is removed, the device switchesfrom the conducting/ON state (where the current I is substantiallygreater than zero) to a non-conducting/OFF state (where current I issubstantially zero) when the charge in the n-type modulation doped QWstructure 24 (and/or the p-type modulation doped QW structure 20)decreases below the holding charge Q_(H). For the vertical cavitysurface detector, the device structure absorbs the optical mode that isreceived vertically through the top surface of the device structure. Forthe whispering gallery microresonator, the device structure absorbs thewhispering gallery mode that circulates in the waveguide region of thewhispering gallery microresonator. For the closed-loop microresonator,the device structure absorbs the optical mode signal that circulates inthe closed-loop waveguide of the closed-loop microresonator.

In alternate configurations based upon the vertical cavity surfaceemitting laser/detector as described above, a diffraction grating can beformed in the top mirror over the active device structure describedabove. For the laser, the diffraction grating performs the function ofdiffracting light produced within the resonant vertical cavity intolight propagating laterally in a waveguide which has the top DBR mirrorand bottom DBR mirror 12 as waveguide cladding layers and which haslateral confinement regions. For the detector, the diffraction gratingperforms the function of diffracting incident light that is propagatingin the lateral direction into a vertical cavity mode, where it isabsorbed resonantly in the vertical resonant cavity.

Details of examples of these device structures and specifics ofexemplary layer structures utilizing group III-V materials are describedin U.S. application Ser. No. 13/921,311, filed on Jun. 19, 2013, andIntern. Pat. Appl. No. PCT/US2012/051265, filed on Aug. 17, 2012, whichare commonly assigned to assignee of the present application and hereinincorporated by reference in their entireties.

FIGS. 2A-2B illustrate an embodiment of a whispering gallerymicroresonator 200 realized as part of an optoelectronic integratedcircuit that employs the layer structure of FIG. 1. The whisperinggallery microresonator 200 is a bottom diode laser or optical detectoras describe above. Thus, it can be configured as a laser or as anoptical detector. In this embodiment, the whispering gallerymicroresonator 200 includes a mesa 212 that is formed by etching thelayer structure of FIG. 1 to a depth near the top of layer 22, and thenpatterning and etching the resultant structure to define the innerannular sidewall 213 that forms the circular profile of the mesa 212 asevident from FIG. 2A. The inner sidewall 213 extends to an intermediatemesa 214 formed in the layer structure in spacer layer(s) 22 above (butnear) the p-type modulation doped quantum well structure 20. Theintermediate mesa 214 has an annular profile as defined by the annularsidewall 213 and an annular sidewall 215 (which is offset radiallyinside the sidewall 213) as shown in FIG. 2B.

Two ion implant regions 216, 218 are defined by ion implantation throughthe intermediate mesa 214. The ion implant regions 216, 218 are similarto the ion implant regions 719 and 721 of the p-channel HFET asdescribed above with respect to FIG. 7 and can be implanted togetherwith these implants with the same ions species (i.e., p-type acceptorions for the ion implant region 216 and oxygen species for the ionimplant region 218) as described above. The implant region 216 isimplanted to a depth that encompasses the p-type modulation doped QWstructure 20 with an annular pattern that is disposed laterally insidethe projection of the annular sidewall 213 as evident from FIG. 2B. Theimplant region 216 provides for electrical contact to the annular p-typemodulation doped QW structure 20 that surrounds the implant region 216.The ion implant region 218 (which has the deepest depth of the twoimplant regions) is implanted into the N+-type layer(s) 14 with apattern that is disposed laterally inside the projection of the annularsidewall 213 as evident from FIG. 2B. In this manner, the implant region216 overlies the implant region 218. The high resistance deep oxygen ionimplant region 218 effectively blocks current flow therethrough and thusoperates to funnel or steer current into the active region of theresonant cavity of the device. Furthermore, the current blocking oxygenion implant region 218 defines an isolation region between the p-typeimplant region 216 and the bottom N+-type ohmic contact layer 14 of thelayer structure. Such isolation region is substantially devoid ofconducting species and significantly reduces the capacitance between theanode terminal electrode 222 and the cathode terminal electrode 224 ofthe device. This capacitance can drastically lower the speed of responseof the device if not reduced.

The resultant structure is patterned and etched to form the annularsidewall 215 that extends downward to a central bottom mesa 220 formedin the bottom ohmic contact layer 14. The bottom mesa 220 has a circularprofile as defined by the annular sidewall 215 as best shown in FIG. 2A.This etching step can also remove the central portion of the implantregions 216 and 218 such that they each have an annular profile disposedlaterally between the annular sidewall 215 and the projection ofsidewall 213 as shown in FIG. 2B.

An anode terminal electrode 222 is formed on the intermediate mesa 214with an annular pattern that is offset laterally inside the annularsidewall 213 as best shown in FIGS. 2A and 2B. The anode terminalelectrode 222 contacts the p-type ion implant regions 216, which contactthe p-type modulation doped QW structure 20 of the device structure. Acathode terminal electrode 224 is formed on the bottom mesa 220 incontact with the bottom n-type ohmic contact layer(s) 14 as best shownin FIG. 2B. The cathode terminal electrode 224 can be patterned as acircular tab as best shown in FIG. 2A or can have some other shape.Similar to the source, drain and gate terminal electrodes of thep-channel HFET device as described above with respect to FIGS. 7A and7B, the metal of the anode terminal electrode 222 is preferably an Au—Bealloy, and the metal of the cathode terminal electrode 224 is preferablyan Au—Ge—Ni alloy. The resultant structure can be heated to treat themetal alloys of the source, drain and gate electrodes as desired. In oneembodiment, the resultant structure can be heated at 420° C. to treatthe metal alloys of the anode and cathode electrodes of the device. Suchmetallization can be carried out in tandem with the metallization of thesource, drain and gate electrodes of the p-channel HFET device asdescribed above with respect to FIGS. 7A and 7B or the electrode ofother devices integrally formed on the substrate 10.

Following the metallization, the resultant structure is patterned andetched to form sidewalls 226 that extend from the top mesa 212 to themirror layers 12. One of the sidewalls 226-1 forms the outer annularperiphery of the top mesa 212. Two other sidewalls 226-2 and 226-3 forma waveguide rib that defines a coupling waveguide 230 extendingtangential to the outer annular sidewall 226-1 of the resonator deviceas best shown on FIG. 2A. The sidewall 226-2 of the coupling waveguide230 is offset from the annular sidewall 226-1 by a narrow gap 232 andthe height of the coupling waveguide 230 can match the height of themesa 212 as best shown in FIG. 2B.

A trench etch can expose the bottom mirror layers 12 in the vicinity ofboth the whispering gallery microresonator 200 and the couplingwaveguide 230. The exposed bottom mirror layers 12 can be oxidized insteam ambient. A dielectric top mirror (not shown) can cover the topmesa 212 and the annular sidewalls of the microresonator 200 and thecoupling waveguide 230. The dielectric material of the top mirror canfill the gap 232.

The index changes provided by the top mesa 212 (together with the topmirror when present), the inner annular sidewall 213, the outer annularsidewall 226-1, the ion implant regions 216, 218, and the bottom DBRmirror 12 form a resonant cavity with an disk-shaped annular volume thatis configured to support a whispering gallery optical mode signal. Thethickness of the disk-shaped annular volume can be configured tocorrespond to at or near one wavelength (for example, a thickness at ornear 1 μm for a whispering gallery optical mode signal in thenear-infrared range of the electromagnetic spectrum). The thickness ofthe disk-shaped annular volume can encompass relatively equal portionsof the layer structure of FIG. 1 above and below the p-type modulationdoped quantum well structure 20. The coupling waveguide 230 provides forevanescent coupling of light to and/or from the resonant cavity of thewhispering gallery microresonator device 200. Electrically, thewhispering gallery microresonator device 200 can operate as anelectrically-pumped bottom diode laser or bottom diode detector.

For the bottom diode laser, the anode terminal electrode 222 is forwardbiased relative to the cathode terminal electrode 224 such that holesare injected from the anode terminal electrode 222 into the QWchannel(s) realized in the p-type modulation doped QW structure 20 inorder to induce photon emission within the device structure. Thecurrent-blocking ion implant region 218 funnels the injected holecurrent that flow from the anode terminal electrode 222 and the p-typecontact implant region 216 into the QW channel of the p-type modulationdoped QW structure 20 within the annular volume of the resonant cavityof the device. Such current funneling enhances the current density ofthe injected current in the QW channel of the p-type modulation doped QWstructure 20 within the annular volume of the resonant cavity of thedevice, which can improve the output power of the device and/or lowerthe laser threshold voltage of the device.

For the diode detector, the anode terminal electrode 222 is reversedbiased relative to the cathode terminal electrode 224. An input opticallight is supplied to the coupling waveguide 230, which couples the inputoptical light as a whispering gallery mode signal that propagates in theannular resonant cavity of the whispering gallery microresonator device200 for absorption by the device structure. The reverse bias conditionsof the anode terminal electrode 222 and the cathode terminal electrode224 are configured such the diode detector produces photocurrent betweenthe anode terminal electrode 222 and the cathode terminal electrode 224that is proportional to the intensity of the whispering gallery opticalmode absorbed by the device structure. The photocurrent flows betweenthe anode terminal 222 and cathode terminal 224 under the reverse bias.The current-blocking ion implant region 218 substantially reduces darkleakage current, which can greatly reduce the sensitivity of the deviceif not addressed.

FIGS. 3A-3B illustrate an embodiment of a closed-loop (ring)microresonator 300 realized as part of an optoelectronic integratedcircuit that employs the layer structure of FIG. 1. The ringmicroresonator 300 is a bottom diode laser or optical detector asdescribed above. Thus, it can be configured as a laser or as an opticaldetector. In this embodiment, the ring microresonator 300 includes a topmesa 311, an intermediate mesa 312 that is surrounded by the top mesa311, and a central bottom mesa 313 that is surrounded by theintermediate mesa 312. The top mesa 311 is formed by the top surface oflayer 30 of the layer structure of FIG. 1. The intermediate mesa 312 isformed by patterning and etching the layer structure to a depth inspacer layer(s) 22 above (but near) the p-type modulation doped quantumwell structure 20 to define the annular sidewall 314 that forms theouter circular profile of the mesa 312 as evident from FIG. 3A. Thesidewall 314 extends to the intermediate mesa 313 formed in the layerstructure in the spacer layer(s) 22 above (but near) the p-typemodulation doped quantum well structure 20. The intermediate mesa 312has an annular profile as defined by the annular sidewall 314 and anannular sidewall 315 (which is offset radially inside the sidewall 314)as shown in FIG. 3B.

Two ion implant regions 316, 318 are defined by ion implantation throughthe intermediate mesa 312. The ion implant regions 316, 318 are similarto the ion implant regions 719 and 721 of the p-channel HFET asdescribed above with respect to FIG. 7 and can be implanted togetherwith these implants with the same ions species (i.e., p-type acceptorions for the ion implant region 316 and oxygen species for the ionimplant region 318) as described above. The implant region 316 isimplanted to a depth that encompasses the p-type modulation doped QWstructure 20 with an annular pattern that is disposed laterally insidethe projection of the annular sidewall 314 as evident from FIG. 3B. Theimplant region 316 provides for electrical contact to the annular p-typemodulation doped QW structure 20 that surrounds the implant region 316.The ion implant region 318 (which has the deepest depth of the twoimplant regions) is implanted into the N+-type layer 14 with a patternthat is disposed laterally inside the projection of the annular sidewall314 as evident from FIG. 3B. In this manner, the implant region 316overlies the implant region 318. The high resistance deep oxygen ionimplant region 318 effectively blocks current flow therethrough and thusoperates to funnel or steer current into the active region of theresonant cavity of the device. Furthermore, the current blocking oxygenion implant region 318 defines an isolation region between the p-typeimplant region 316 and the bottom N+-type ohmic contact layer 14 of thelayer structure. Such isolation region is substantially devoid ofconducting species and significantly reduces the capacitance between theanode terminal electrode 322 and the cathode terminal electrode 324 ofthe device. This capacitance can drastically lower the speed of responseof the device if not reduced.

The resultant structure is patterned and etched to form the annularsidewall 315 that extends downward to the bottom mesa 313 formed in thebottom ohmic contact layer 14. The bottom mesa 313 has a circularprofile as defined by the annular sidewall 313 as best shown in FIG. 3A.This etching step can also remove the central portion of the implantregions 316 and 318 such that they each have an annular profile disposedlaterally between the annular sidewall 315 and the projection ofsidewall 314 as shown in FIG. 3B.

An anode terminal electrode 322 is formed on the intermediate mesa 312with an annular pattern that is offset laterally inside the annularsidewall 314 as best shown in FIGS. 3A and 3B. The anode terminalelectrode 322 contacts the p-type ion implant regions 316, which contactthe p-type modulation doped QW structure 20 of the device structure. Acathode terminal electrode 324 is formed on the bottom mesa 313 incontact with the bottom n-type ohmic contact layer(s) 14 as best shownin FIG. 3B. The cathode terminal electrode 224 can be patterned as acircular tab as best shown in FIG. 3A or can have some other shape.Similar to the source, drain and gate terminal electrodes of thep-channel HFET device as described above with respect to FIGS. 7A and7B, the metal of the anode terminal electrode 322 is preferably an Au—Bealloy, and the metal of the cathode terminal electrode 324 is preferablyan Au—Ge—Ni alloy. The resultant structure can be heated to treat themetal alloys of the source, drain and gate electrodes as desired. In oneembodiment, the resultant structure can be heated at 420° C. to treatthe metal alloys of the anode and cathode electrodes of the device. Suchmetallization can be carried out in tandem with the metallization of thesource, drain and gate electrodes of the p-channel HFET device asdescribed above with respect to FIGS. 7A and 7B or the electrode ofother devices integrally formed on the substrate 10.

Following the metallization, the resultant structure is patterned andetched to form sidewalls 326 that extend from the top mesa 311 to themirror layers 12. One of the sidewalls 326-1 forms the outer annularperiphery of the top mesa 311. Two other sidewalls 326-2 and 326-3 forma waveguide rib that defines a coupling waveguide 330 extendingtangential to the outer annular sidewall 326-1 of the resonator device300 as best shown on FIG. 3A. The sidewall 326-2 of the couplingwaveguide 330 is offset from the annular sidewall 326-1 by a narrow gap332 and the height of the coupling waveguide 330 can match the height ofthe mesa 31 as best shown in FIG. 3B.

A trench etch can expose the bottom mirror layers 12 in the vicinity ofboth the ring microresonator 300 and the coupling waveguide 330. Theexposed bottom mirror layers 12 can be oxidized in steam ambient. Adielectric top mirror (not shown) can cover the top mesa 311 and theannular sidewalls of the resonator 300 and the coupling waveguide 330.The dielectric material of the top mirror can fill the gap 332.

The index changes provided by the top mesa 311 (together with the topmirror when present), the inner annular sidewall 314, the outer annularsidewall 326-1, the ion implant regions 316, 318, and the bottom DBRmirror 12 form a resonant cavity with a ring-shaped annular volume thatis configured to support circulating propagation of an optical modesignal about the ring-shaped volume. The length of the optical path ofthe ring-shaped annular volume of the resonant cavity is tuned to theparticular wavelength of the optical mode signal that is to propagate inthe resonant cavity. Specifically, the length L of the optical path isselected to conform to the following:

$\begin{matrix}{L = \frac{2\pi \; m\; \lambda_{c}}{n_{eff}}} & (1)\end{matrix}$

-   -   where m is an integer greater than zero;        -   λ_(c) is the wavelength of the optical mode signal that            propagates in ring-shaped annular volume of the resonant            cavity; and        -   n_(eff) is the effective refractive index of the ring-shaped            annular volume of the resonant cavity.            The width of the ring-shaped annular volume of the resonant            cavity (i.e., the radial offset between the annular            sidewalls 314, 326-1) can be less than 2 μm, and possibly 1            μm or less. The thickness of the ring-shaped annular volume            can be configured to correspond to at or near one wavelength            (for example, a thickness at or near 1 μm for an optical            mode signal in the near-infrared range of the            electromagnetic spectrum). The thickness of the ring-shaped            annular volume can encompass relatively equal portions of            the layer structure of FIG. 1 above and below the p-type            modulation doped quantum well structure 20. The coupling            waveguide 330 provides for evanescent coupling of light to            and/or from the resonant cavity of the ring microresonator            device 300. Electrically, the ring microresonator device 300            can operate as an electrically-pumped bottom diode laser or            bottom diode detector.

For the bottom diode laser, the anode terminal electrode 322 isforwarded biased relative to the cathode terminal electrode 324 suchthat holes are injected from the anode terminal electrode 322 into theQW channel(s) realized in the p-type modulation doped QW structure 20 inorder to induce photon emission within the device structure. Thecurrent-blocking ion implant region 318 funnels or steers the injectedhole current that flows from the anode terminal electrode 322 and thep-type contact implant region 316 into the QW channel of the p-typemodulation doped QW structure 20 within the ring-shaped annular volumeof the resonant cavity of the device. Such current funneling or steeringenhances the current density of the injected current in the QW channelof the p-type modulation doped QW structure 20 within the ring-shapedannular volume of the resonant cavity of the device, which can improvethe output power of the device and/or lower the laser threshold voltageof the device.

For the diode detector, the anode terminal electrode 322 is reversedbiased relative to the cathode terminal electrode 324. An input opticallight is supplied to the coupling waveguide 330, which couples the inputoptical light as an optical mode signal that circulates in thering-shaped annular resonant cavity of the ring microresonator device300 for absorption by the device structure. Under reverse biasconditions the anode terminal electrode 322 and the cathode terminalelectrode 324 are configured such the diode detector producesphotocurrent between the anode terminal electrode 322 and the cathodeterminal electrode 324 that is proportional to the intensity of theoptical mode signal absorbed by the device structure. The photocurrentflows between the anode terminal 322 and cathode terminal 324 under thereverse bias. The current-blocking ion implant region 318 substantiallyreduces dark leakage current, which can greatly reduce the sensitivityof the device if not addressed.

FIGS. 4A-4B illustrate an embodiment of a whispering gallery thyristormicroresonator 400 realized as part of an optoelectronic integratedcircuit that employs the layer structure of FIG. 1. The whisperinggallery thyristor microresonator 400 is a thyristor laser or opticaldetector as describe above. Thus, it can be configured as a laser or asan optical detector. In this embodiment, the whispering gallerythyristor microresonator 400 includes a top mesa 411, a firstintermediate mesa 412 that is disposed outside the outer periphery ofthe top mesa 411, a second intermediate mesa 413 that is disposedoutside the outer periphery of the first intermediate mesa 412, a thirdintermediate mesa 414 that is disposed inside the inner periphery of thetop mesa 411, and a central bottom mesa 415 that is disposed inside theinner periphery of the third intermediate mesa 414.

The top mesa 411 is formed by the top surface of layer 30 of the layerstructure of FIG. 1. An anode terminal electrode 423 is formed on thetop mesa 411 with an annular pattern as best shown in FIGS. 4A and 4B.The anode terminal electrode 423 contacts the top p-type ohmic contactlayer 30. The metal of the anode terminal electrode 423 can be tungstenor other suitable metal or alloy. The metal of the anode terminalelectrode 423 can be patterned by a lift off by oxide process asdescribed below with respect to FIGS. 9A-9D.

The first intermediate mesa 412 is formed by patterning and etching thelayer structure to a depth in layer(s) 26 above (but near) the n-typemodulation doped quantum well structure 24 to define the annularsidewall 416 that forms the inner circular profile of the mesa 412 asevident from FIG. 4A. The sidewall 416 extends to the first intermediatemesa 412 formed in the layer structure in the layer(s) 26 above (butnear) the n-type modulation doped quantum well structure 24. The firstintermediate mesa 412 has an annular profile as defined by the annularsidewall 416 and an annular sidewall 417 (which is offset radiallyoutside the sidewall 416) as shown in FIG. 4B. The patterned metal ofthe anode terminal electrode 423 can be used as a mask layer for theetch of the sidewall 416 if desired

The second intermediate mesa 413 is formed by patterning and etching thelayer structure to a depth near the middle of spacer layer(s) 22 todefine the annular sidewall 417 that forms the inner circular profile ofthe second intermediate mesa 413 as evident from FIG. 4A. The sidewall417 extends to the second intermediate mesa 413 formed in the layerstructure near the middle of the spacer layer(s).

The third intermediate mesa 414 is formed by patterning and etching thelayer structure to a depth in spacer layer(s) 22 above (but near) thep-type modulation doped quantum well structure 20 to define the annularsidewall 418 that forms the outer circular profile of the thirdintermediate mesa 414 as evident from FIG. 4A. The sidewall 418 extendsto the third intermediate mesa 414 formed in the layer structure in thespacer layer(s) 22 above (but near) the p-type modulation doped quantumwell structure 20. The third intermediate mesa 414 has an annularprofile as defined by the annular sidewall 418 and an annular sidewall419 (which is offset radially inside the sidewall 418) as shown in FIG.4B. The patterned metal of the anode terminal electrode 423 can be usedas a mask layer for the etch of the sidewall 418 if desired

An ion implant region 420 is defined by ion implantation of n-type ionsthrough the first intermediate mesa 412. The ion implant 420 isimplanted to a depth that encompasses the n-type modulation doped QWstructure 24 with an annular pattern that is disposed laterally outsidethe projection of the annular sidewall 416 as evident from FIG. 4B. Theimplant region 420 provides for electrical contact to the annular n-typemodulation doped QW structure 24 that surrounds the implant region 420.

Two ion implant regions 421, 422 are defined by ion implantation throughthe intermediate mesa 414. The ion implant regions 421, 422 are similarto the ion implant regions 719 and 721 of the p-channel HFET asdescribed above with respect to FIG. 7 and can be implanted togetherwith these implants with the same ions species (i.e., p-type acceptorions for the ion implant region 421 and oxygen species for the ionimplant region 422) as described above. The implant region 421 isimplanted to a depth that encompasses the p-type modulation doped QWstructure 20 with an annular pattern that is disposed laterally insidethe projection of the annular sidewall 418 as evident from FIG. 4B. Theimplant region 421 provides for electrical contact to the annular p-typemodulation doped QW structure 20 that surrounds the implant region 421.The ion implant region 422 (which has the deepest depth of the twoimplant regions) is implanted into the N+-type layer 14 with a patternthat is disposed laterally inside the projection of the annular sidewall418 as evident from FIG. 4B. In this manner, the implant region 421overlies the implant region 422. The high resistance deep oxygen ionimplant region 422 effectively blocks current flow therethrough and thusoperates to funnel or steer current into the active region of theresonant cavity of the device. Furthermore, the current blocking oxygenion implant region 422 defines an isolation region between the p-typeimplant region 421 and the bottom N+-type ohmic contact layer 14 of thelayer structure. Such isolation region is substantially devoid ofconducting species and significantly reduces the capacitance between thep-channel injector terminal electrode 425 and the cathode terminalelectrode 426 of the device. This capacitance can drastically lower thespeed of response of the device if not reduced.

The resultant structure is patterned and etched to form the annularsidewall 419 that extends downward to the central bottom mesa 415 formedin the bottom ohmic contact layer 14. The bottom mesa 415 has a circularprofile as defined by the annular sidewall 419 as best shown in FIG. 4A.This etching step can also remove the central portion of the implantregions 421 and 422 such that they each have an annular profile disposedlaterally between the annular sidewall 419 and the projection ofsidewall 418 as shown in FIG. 4B.

An n-channel injector terminal electrode 424 is formed on the firstintermediate mesa 412 as best shown in FIGS. 4A and 4B. The n-channelinjector terminal electrode 424 contacts the n-type ion implant region420, which contacts the n-type modulation doped QW structure 24 of thedevice structure. A p-channel injector terminal electrode 425 is formedon the third intermediate mesa 414 with an annular pattern as best shownin FIGS. 4A and 4B. The p-channel injector terminal electrode 425contacts the p-type ion implant region 422, which contacts the p-typemodulation doped QW structure 20 of the device structure. A cathodeterminal electrode 426 is formed on the bottom mesa 415 in contact withthe bottom n-type ohmic contact layer(s) 14 as best shown in FIG. 4B.The cathode terminal electrode 426 can be patterned as a circular tab asbest shown in FIG. 4A or can have some other shape. Similar to thesource, drain, gate and collector terminal electrodes of the p-channelHFET device as described above with respect to FIGS. 7A and 7B, themetal of the p-channel injector terminal electrode 425 is preferably anAu—Be alloy, and the metal of the n-channel injector terminal 424 andthe cathode terminal electrode 426 is preferably an Au—Ge—Ni alloy. Theresultant structure can be heated to treat the metal alloys of theelectrodes of the device as desired. In one embodiment, the resultantstructure can be heated at 420° C. to treat the metal alloys of thedevice. Such metallization can be carried out in tandem with themetallization of the source, drain and gate electrodes of the p-channelHFET device as described above with respect to FIGS. 7A and 7B or theelectrode(s) of other devices integrally formed on the substrate 10.

Following the metallization, the resultant structure is patterned andetched to form sidewalls 427 that extend from the second intermediatemesa 413 to the mirror layers 12. One of the sidewalls 427-1 forms theouter annular periphery of the resonator device such that the secondintermediate mesa 413 of the resonator device 400 has an annular profileas defined by the annular sidewall 417 and the annular sidewall 427-1(which is offset radially outside the sidewall 417) as shown in FIG. 4B.Two other sidewalls 427-2 and 427-3 form a waveguide rib that defines acoupling waveguide 430 extending tangential to the outer annularsidewall 427-1 of the resonator device 400 as best shown on FIG. 4A. Thesidewall 427-2 of the coupling waveguide 430 is offset from the annularsidewall 427-1 by a narrow gap 432 and the height of the couplingwaveguide 440 can match the height of the mesa 413 of the resonatordevice 400 as best shown in FIG. 4B.

A trench etch can expose the bottom mirror layers 12 in the vicinity ofboth the thyristor whispering gallery microresonator 400 and thecoupling waveguide 430. The exposed bottom mirror layers 12 can beoxidized in steam ambient. A dielectric top mirror (not shown) can coverthe mesas 413, 412, 411 and the annular sidewalls of the resonator 400and the coupling waveguide 430. The dielectric material of the topmirror can fill the gap 432.

The index changes provided by the mesa 413 (together with the top mirrorwhen present), the inner annular sidewall 418, the outer annularsidewall 427-1, the ion implant regions 421, 422, and the bottom DBRmirror 12 form a resonant cavity with a disk-shaped annular volume thatis configured to support a whispering gallery optical mode signal. Thethickness of the disk-shaped annular volume can be configured tocorrespond to at or near one wavelength (for example, a thickness at ornear 1 μm for a whispering gallery optical mode signal in thenear-infrared range of the electromagnetic spectrum). The thickness ofthe disk-shaped annular volume can encompass relatively equal portionsof the layer structure of FIG. 1 above and below the p-type modulationdoped quantum well structure 20. The coupling waveguide 430 provides forevanescent coupling of light to and/or from the resonant cavity of thethyristor whispering gallery microresonator device 400. Electrically,the thyristor whispering gallery microresonator device 400 can operateas an electrically-pumped thyristor laser or thyristor detector.

For the thyristor laser, the device structure switches from anon-conducting/OFF state (where the current I through the device issubstantially zero) to a conducting/ON state (where current I issubstantially greater than zero) when i) the anode terminal electrode423 is forward biased with respect to the cathode terminal electrode 426and ii) the voltage between n-channel injector 424 and the anodeelectrode 423 is biased such that charge is produced in the n-typemodulation doped QW structure 24 that is greater than the criticalswitching charge Q_(CR), which is that charge that reduces the forwardbreakdown voltage such that no off state bias point exists. The voltagebetween p-channel injector electrode 425 and the cathode electrode 426can also be configured to produce a charge in the p-type modulationdoped QW structure 20 that is greater than the critical switching chargeQ_(CR). The critical switching charge Q_(CR) is unique to the geometriesand doping levels of the device. The device switches from theconducting/ON state (where the current I is substantially greater thanzero) to a non-conducting/OFF state (where current I is substantiallyzero) when the current I through device falls below the hold current ofthe device for a sufficient period of time such that the charge in then-type modulation doped QW structure 24 (or the charge in the p-typemodulation doped QW structure 20) decreases below the holding chargeQ_(H), which is the critical value of the channel charge which willsustain holding action. Thus, if the anode terminal 423 is forwardbiased with respect to the cathode terminal 426 and the n-channelinjector terminal 424 (and/or the p-channel injector terminal 425) isbiased to produce the critical switching charge Q_(CR) in the n-typemodulation doped QW structure 24 (or in the p-type modulation doped QWstructure 20), then the device will switch to its conducting/ON state.If the current I in the conducting/ON state is above the threshold forlasing I_(TH), then photon emission will occur within the devicestructure. For the microresonator 400, such photon emission produces thewhispering gallery mode signal that circulates in the resonant cavity ofthe microresonator 400, which is coupled to the coupling waveguide 430to produce an output optical signal that propagates in the couplingwaveguide 430 for output therefrom. The current-blocking ion implantregion 421 funnels the current that flows from between the anodeterminal electrode 423 and the cathode terminal electrode 426 into theQW channel of the p-type modulation doped QW structure 20 within thedisk-shaped annular volume of the resonant cavity of the device. Suchcurrent funneling enhances the current density of the injected currentin the QW channel of the p-type modulation doped QW structure 20 withinthe disk-shaped annular volume of the resonant cavity of the device,which can improve the output power of the device and/or lower the laserthreshold voltage of the device.

For the thyristor detector, an input optical signal is supplied to thecoupling waveguide 430, which couples the input optical signal as awhispering gallery mode optical signal that circulates in the resonantcavity of the microresonator device 400 for absorption by the devicestructure. The device structure switches from a non-conducting/OFF state(where the current I through the device is substantially zero) to aconducting/ON state (where current I is substantially greater than zero)in response to the whispering gallery mode optical signal producingcharge in the n-type modulation doped QW structure 24 and/or the p-typemodulation doped QW structure 20 resulting from photon absorption of thewhispering gallery mode optical signal. Specifically, the anode terminalelectrode 423 is forward biased with respect to the cathode terminalelectrode 426 and the voltage between n-channel injector 424 and theanode electrode 423 (and/or the voltage between the p-channel injector425 and the cathode terminal electrode 626) is biased such that thatcharged produced in the n-type modulation doped QW structure 24 (and/orthe p-type modulation doped QW structure 20) resulting from photonabsorption of the whispering gallery mode optical signal is greater thanthe critical switching charge Q_(CR). When the whispering gallery modeoptical signal is removed, the device switches from the conducting/ONstate (where the current I is substantially greater than zero) to anon-conducting/OFF state (where current I is substantially zero) whenthe charge in the n-type modulation doped QW structure 24 (and/or thep-type modulation doped QW structure 20) decreases below the holdingcharge Q_(H).

For both the thyristor laser and the thyristor detector, thecurrent-blocking ion implant region 421 reduces the capacitance betweenthe p-channel injector terminal electrode 425 and the cathode terminalelectrode 426 of the device. This capacitance can drastically lower thespeed of response of the device if not reduced.

FIGS. 5A-5E illustrate a configuration of a closed-loop microresonator500 that can be made utilizing the layer structure of FIG. 1, whichincludes a resonator 501 spaced from a section of a zig-zag waveguidestructure 509 by a gap region 513. The zig-zag waveguide structure 509is optically coupled to the resonator 501 by evanescent-wave couplingover the gap region 513. The resonator 501 defines a resonant cavity,which is referred to herein as active waveguide 502, that follows aclosed path that is generally rectangular in shape. The optical pathlength of the active waveguide 502 is tuned to the particular wavelengthof the optical mode signal 504 that is to propagate in the waveguide502. Specifically, the length of the rectangular closed path of theactive waveguide 502 is given as 2(L₁+L₂) and the L₁ and L₂ parametersare selected to conform to the following:

$\begin{matrix}{{2\left( {L_{1} + L_{2}} \right)} = \frac{2\pi \; m\; \lambda_{D}}{n_{eff}}} & (2)\end{matrix}$

where L₁ and L₂ are the effective lengths of the opposed sides of theactive waveguide 502;

-   -   m is an integer greater than zero;    -   λ_(D) is the wavelength of the optical mode 504 that is to        propagate in the active waveguide 502; and    -   n_(eff) is the effective refractive index of the active        waveguide 502.        The width (W) of the active waveguide 502 can be less than 2 μm,        and possibly 1 μm or less. The width of the gap region 513        (i.e., the spacing between the active waveguide 502 and the        zig-zag waveguide 509) can be less than 2 μm, and possibly on        the order of 1 μm or less.

The optical mode 504 circulates around the active waveguide 502 and isstrongly confined within the active waveguide 502 by internal reflectionat the reflective interfaces of the active waveguide 502. The zig-zagwaveguide 509 defines a passive rib waveguide that forms a zig-zag path.The optical mode is strongly confined within the zig-zag waveguide 509by internal reflection at the reflective interfaces of the zig-zagwaveguide 509. The active waveguide 502 can be logically partitioned infour sections that are coupled to one another by ninety-degree cornersas shown in FIG. 5A. The four sections include a straight section 503Athat extends parallel to and is closely-spaced from a straight section511 of the zig-zag waveguide 509 by the gap region 513, a straightsection 503B disposed opposite the straight section 503A, and twostraight sections 503C and 503D that are opposed to one another and thatextend orthogonal to the sections 503A and 503B between thecorresponding opposed ends of the sections 503A and 503B. Section 503Ais configured to provide evanescent coupling to (or from) the straightsection 511 of the zig-zag waveguide 509 for the optical mode signal 504that circulates in the active waveguide 502. Sections 503B and 503C areconfigured to contribute to the generation (or absorption) of theoptical mode signal 504 that circulates in the active waveguide 502.Section 503D has a number of portions that perform different functions.Specifically, section 503D has two opposed end portions 505A, 505B thatare configured in a manner similar to sections 503B and 503C tocontribute to the generation (or absorption) of the optical mode signal504 that circulates in the active waveguide 502. Segment 503D also has acentral portion 507 that is electrically isolated from the two opposedend portions 505A, 505B by corresponding passive waveguide portions 509Aand 509B as shown. The central portion 507 is configured to providetuning of the wavelength of the optical mode signal 504 that circulatesin the active waveguide 502.

FIG. 5B is a cross-sectional schematic view of section 503C of theactive waveguide 502. All of the features of the cross-section extendlaterally along the length of section 503C as evident from FIG. 5A. Inthis description, “inner” refers to features that are closer to thecenter of the waveguide 502, and “outer” refers to features that arefurther away from the center of the waveguide 502. These featuresinclude a top mesa 515 defined between an inner sidewall 517A and anouter sidewall 517B. Ion implant regions 516A, 516B (preferably ofn-type ions) can be implanted to a depth within the top layers 26, 28,30 on opposite sides of waveguide 502 adjacent the respective sidewalls517A, 517B as shown. The waveguide ion implant regions 516A, 516B canprovide an index change that operates to aid in confining and guidingthe optical mode signal 504 that propagates within the central region ofthe waveguide 502. The inner sidewall 517A extends downward to an innermesa 519A (which extends laterally to an inner sidewall 521A), while theouter sidewall 517B extends downward to an outer mesa 519B (whichextends laterally to an outer sidewall 521A). Both the inner mesa 519Aand the outer mesa 519B are formed in the layer structure in spacerlayer(s) 22 above (but near) the p-type modulation doped quantum wellstructure 20. Two implant regions 523A, 525A are defined by ionimplantation through the inner mesa 519A. The ion implant regions 523A,525A are similar to the ion implant regions 719 and 721 of the p-channelHFET as described above with respect to FIG. 7 and can be implantedtogether with these implants with the same ions species (p-type acceptorions for the implant region 523A and oxygen ions for the implant region525A) as described above. The implant region 523A (which has theshallowest depth of the two implant regions 523A, 525A) has a patternthat is disposed laterally between the inner sidewall 521A and theprojection of the inner sidewall 517A as shown in FIG. 5B. The implantregion 523A provides for electrical contact to the p-type modulationdoped QW structure 20. The implant region 525A (which is deeper in depththan the implant region 523A) is implanted into the N+-type layer 14with a pattern that is disposed laterally between the inner sidewall521A and the projection of the inner sidewall 517A as shown in FIG. 5B.In this manner, the implant region 523A overlies the implant region525A. The high resistance deep oxygen ion implant region 525Aeffectively blocks current flow therethrough and defines an isolationregion between the p-type implant region 523A and the bottom N+-typeohmic contact layer 14 of the layer structure. Such isolation region issubstantially devoid of conducting species and significantly reduces thecapacitance between the anode terminal electrode part 533A and thecathode terminal electrode part 531A of the device. This capacitance candrastically lower the speed of response of the device if not reduced.

Similarly, two implant regions 523B, 525B are defined by ionimplantation through the outer mesa 519B. The ion implant regions 523B,525B are similar to the ion implant regions 719 and 721 of the p-channelHFET as described above with respect to FIG. 7 and can be implantedtogether with these implants with the same ions species (p-type acceptorions for the implant region 523B and oxygen ions for the implant region525B) as described above. The implant region 523A (which has theshallowest depth of the two implant regions 523B, 525B) has a patternthat is disposed laterally between the outer sidewall 521B and theprojection of the outer sidewall 517B as shown in FIG. 5B. The implantregion 523B provides for electrical contact to the p-type modulationdoped QW structure 20. The implant region 525B (which is deeper in depththan the implant region 523B) is implanted into the N+-type layer 14with a pattern that is disposed laterally between the outer sidewall521B and the projection of the outer sidewall 517B as shown in FIG. 5B.In this manner, the implant region 523B overlies the implant region525B. The high resistance deep oxygen ion implant region 525Beffectively blocks current flow therethrough and defines an isolationregion between the p-type implant region 523A and the bottom N+-typeohmic contact layer 14 of the layer structure. Such isolation region issubstantially devoid of conducting species and significantly reduces thecapacitance between the anode terminal electrode part 533B and thecathode terminal electrode part 531B of the device. This capacitance candrastically lower the speed of response of the device if not reduced.

The inner sidewall 521A extends downward to an inner bottom mesa 527Aformed in the bottom ohmic contact layer 14. The inner bottom mesa 527Aextends laterally from the inner sidewall 521A to an inner sidewall 529Aas shown in FIG. 5B. The outer sidewall 521B extends downward to anouter bottom mesa 527B formed in the bottom ohmic contact layer 14. Theouter bottom mesa 527B extends laterally from the inner sidewall 521B tothe inner sidewall 529B as shown in FIG. 5B.

Two parts (531A, 531B) of a cathode terminal electrode are formed on theinner and outer bottom mesas 527A, 527B, respectively, in contact withthe bottom n-type ohmic contact layer(s) 14 as best shown in FIG. 5B.Two parts (533A, 533B of an anode terminal electrode are formed on theinner and outer mesas 519A, 519B, respectively, in contact with theirrespective implant regions 525A, 525B. Note that the n-type region ofthe n-type modulation doped QW structure 24 of section 503C floats withrespect to the electrical signals supplied to anode terminal electrodeparts 533A, 533B as well as to the cathode terminal electrode parts531A, 531B. A top mirror 535 can cover the top mesa 515 and thesidewalls 517A, 517B.

The top mesa 515 (or the top mirror 535 when present), the sidewalls517A, 517B and the bottom DBR mirror 12 form part of the closed-pathresonant cavity waveguide that is configured to support circulation ofthe optical mode signal 504 within the resonant cavity waveguide. Thewidth of the resonant cavity waveguide (i.e., the lateral offset betweenthe sidewalls 517A, 517B) can be less than 2 μm, and possibly 1 μm orless. The height of the vertical cavity waveguide can be above sixtypercent of the waveguide width.

FIG. 5C is a cross-sectional schematic view of the tuning portion 507 ofsection 503D of the active waveguide 502. All of the features of thecross-section extend laterally along the length of the tuning portion507 as evident from FIG. 5A. These features include the top mesa 515defined between the inner sidewall 517A and the outer sidewall 517B. Ionimplant regions 516A, 516B (preferably of n-type ions) can be implantedto a depth within the top layers 26, 28, 30 on opposite sides ofwaveguide 502 adjacent the respective sidewalls 517A, 517B as shown. Theion implant regions 516A, 516B can provide an index change that operatesto aid in confining and guiding the optical mode signal 504 thatpropagates within the central region of the waveguide 502. The top mesa515, the sidewalls 517A, 517B and the waveguide implant regions 516A,516B can be extensions of the top mesa, the sidewalls and the waveguideion implant regions that form the resonant rib waveguide of the othersections of the resonator 500. The inner sidewall 517A extends downwardto an inner mesa 559A (which extends laterally to an inner sidewall561A), while the outer sidewall 517B extends downward to an outer mesa559B (which extends laterally to an outer sidewall 561B). Both the innermesa 559A and the outer mesa 559B are formed in the layer structure inspacer layer(s) 22 above (but near) the p-type modulation doped quantumwell structure 20. Implant regions 523A, 525A are defined by ionimplantation through the inner mesa 559A, while implant regions 523B,525B are defined by ion implantation through the outer mesa 559B. Theimplant regions 523A, 525A, 523B, 525B are similar to those describedabove for section 503C of FIG. 5B. The inner sidewall 561A extendsdownward to an inner bottom mesa 567A formed in the bottom ohmic contactlayer 14. The inner bottom mesa 567A extends laterally from the innersidewall 561A to an inner sidewall 569A as shown in FIG. 5C. The outersidewall 561B extends downward to an outer bottom mesa 567B formed inthe bottom ohmic contact layer 14. The outer bottom mesa 567B extendslaterally from the outer sidewall 561B to the outer sidewall 569B asshown in FIG. 5C.

Two parts (571A, 571B) of a first tuning terminal electrode are formedon the inner and outer mesas 559A, 559B, respectively, in contact withtheir respective implant regions 523A, 523B which contact the QW of thep-type modulation doped QW structure 20 of the tuning portion 507. Twoparts (573A, 573B) of a second tuning terminal electrode are formed onthe inner and outer bottom mesas 567A, 567B, respectively, in contactwith the bottom n-type ohmic contact layer(s) 14 of the tuning portion507 as best shown in FIG. 5C. The high resistance deep oxygen ionimplant regions 525A, 525B effectively blocks current flow therethroughand defines isolation regions between the respective p-type implantregions 523A/523B and the bottom N+-type ohmic contact layer 14 of thelayer structure. Such isolation regions are each substantially devoid ofconducting species and significantly reduce the capacitance between thefirst tuning electrode parts 571A, 571B and the cathode terminalelectrode parts 573A, 573B of the device. This capacitance candrastically lower the speed of response of the device if not reduced.Note that the n-type region of the n-type modulation doped QW structure24 of the tuning portion 507 floats with respect to the electricalsignals supplied to tuning electrode parts 571A, 571B, 573A, 573B. A topmirror 535 can cover the top mesa 515 and the sidewalls 517A, 517B.

FIG. 5D is a cross-sectional schematic view of the isolating passivewaveguide portion 509B of section 503D of the active waveguide 502. Allof the features of the cross-section extend laterally along the lengthof the passive waveguide portion 509B as evident from FIG. 5A. Thesefeatures include the top mesa 515 defined between the inner sidewall517A and the outer sidewall 517B. Ion implant regions 516A, 516B(preferably of n-type ions) can be implanted to a depth within the toplayers 26, 28, 30 on opposite sides of waveguide 502 adjacent therespective sidewalls 517A, 517B as shown. The ion implant regions 516A,516B can provide an index change that operates to aid in confining andguiding the optical mode signal 504 that propagates within the centralregion of the waveguide 502. The top mesa 515, the sidewalls 517A, 517Band the waveguide ion implant regions 516A, 516B can be extensions ofthe top mesa, sidewalls and waveguide ion implant regions that form theresonant rib waveguide of the other sections of the resonator 500. Theinner and outer sidewalls 517A extends downward to bottom mirror layers12. A top mirror 535 can cover the top mesa 515 and the sidewalls 517A,517B. Note that the passive waveguide portion 509B is formed adjacentone end of the tuning portion 507, while another passive waveguideportion 509A is formed adjacent the opposed end of tuning portion 507 ofsegment 503D. The passive waveguide portion 509A has the same featuresas passive waveguide portion 509B of FIG. 5D. The opposed passivewaveguide portions 509A and 509B provide electrical isolation of thetuning portion 507 from the two opposed end portions 505A, 505B of theactive waveguide.

FIG. 5E is a cross-sectional schematic view of the coupling section 503Aof the active waveguide 502 and the straight section 511 of the zigzagwaveguide 509 with the gap region 513 therebetween. All of the featuresof the cross-section extend laterally along the length of the tuningportion 507 as evident from FIG. 5A. These features include the top mesa515 defined between inner sidewall 517A and an outer sidewall 517B. Ionimplant regions 516A, 516B (preferably of n-type ions) can be implantedto a depth within the top layers 26, 28, 30 on opposite sides ofwaveguide 502 adjacent the respective sidewalls 517A, 517B as shown. Theion implant regions 516A, 516B can provide an index change that operatesto aid in confining and guiding the optical mode signal 504 thatpropagates within the central region of the waveguide 502. The top mesa515, the sidewalls 517A, 517B and the waveguide ion implant regions516A, 516B can be extensions of the top mesa, sidewalls and waveguideion implant regions that form the resonant rib waveguide of the othersections of the resonator 500. The inner sidewall 517A extends downwardto an inner mesa 519A (which extends laterally to an inner sidewall521A), while the outer sidewall 517B extends downward to the mirrorlayers 12. The inner mesa 519A is formed in the layer structure inspacer layer(s) 22 above (but near) the p-type modulation doped quantumwell structure 20. Implant regions 523A, 525A are defined by ionimplantation through the inner mesa 519A. The implant regions 523A, 525Aare similar to those described above for section 503C of FIG. 5B. Theinner sidewall 521A extends downward to an inner bottom mesa 527A formedin the bottom ohmic contact layer 14. The inner bottom mesa 527A extendslaterally from the inner sidewall 521A and an inner sidewall 569A asshown in FIG. 5E.

A first control electrode 581 is formed on the inner mesas 519A incontact with the implant region 523A, which is in contact with the QW ofthe p-type modulation doped QW structure 20 of the active waveguide 502of the coupling section 503. A second control electrode 583 is formed onthe inner bottom mesa 527A in contact with the bottom n-type ohmiccontact layer(s) 14 of the active waveguide 502 of the coupling section503 as best shown in FIG. 5E. The high resistance deep oxygen ionimplant region 525A effectively blocks current flow therethrough anddefines an isolation region between the p-type implant region 523A andthe bottom N+-type ohmic contact layer 14 of the layer structure. Suchisolation region is substantially devoid of conducting species andsignificantly reduces the capacitance between the first controlelectrode 581 and the second control electrode 583 of the device. Thiscapacitance can drastically lower the speed of response of the device ifnot reduced. Note that the n-type region of the n-type modulation dopedQW structure 24 floats with respect to the electrical signals suppliedto first control terminal electrode 581.

The straight section 511 of the zig-zag waveguide 509 is formed from thelayer structure of FIG. 1 by patterning and etching the layer structureto form opposed sidewalls 581-1 and 585-2 that extend from the topsurface 501 to the mirror layers 12. The sidewall 585-1 of the straightsection 511 is offset from the sidewall 517B of the coupling section503A by the gap region 513 as shown. A top mirror (not shown) can coverthe top mesa 515 and the sidewalls of the devices.

The etching that forms the sidewalls and mesas of the sections of theresonator 501 and the coupling waveguide 509, the ion implantationoperations and associated RTA operations for the sections of thesections of the resonator 501 and the coupling waveguide 509, as well asthe metallization of the terminal electrodes of the resonator 501 can becarried in tandem with the formation of like structures in other devicesintegrally formed on the substrate 10.

Electrically, certain portions of the resonator 501 (i.e., sections505A, 505B, 503B, and 503C) can operate as an electrically-pumped bottomdiode laser or bottom diode detector.

For the bottom diode laser, the anode terminal electrode (parts 533A,533B) is forwarded biased relative to the cathode terminal electrode(parts 531A, 531B) such that holes are injected from the anode terminalelectrode (parts 533A, 533B) into the QW channel(s) realized in thep-type modulation doped QW structure 20 in order to induce photonemission within the waveguide 502 of the device structure. Thecurrent-blocking deep oxygen ion implant regions ion implant regions525A, 525B can aid in funneling the injected hole current that flowsfrom the anode terminal electrode parts 533A, 533B and the p-typecontact implant regions 525A, 525B into the QW channel of the p-typemodulation doped QW structure 20 within the waveguide 502 of the devicestructure. Such current funneling enhances the current density of theinjected current in the QW channel of the p-type modulation doped QWstructure 20 within the waveguide 502 of the device structure, which canimprove the output power of the device and/or lower the laser thresholdcurrent and voltage of the device. The deep oxygen ion implant regions525A, 525B define isolation regions that significantly reduce thecapacitance between the anode terminal electrode (parts 533A, 533B) andthe cathode terminal electrode (parts 531A, 531B). This capacitance candrastically lower the speed of response of the device if not reduced.

For the diode detector, the anode terminal electrode (parts 533A, 533B)is reversed biased relative to the cathode terminal electrode (parts(531A, 531B). An input optical light is supplied to the couplingwaveguide 509, which couples the input optical light as an optical modesignal 504 that propagates in the waveguide 502 of the resonator 501 forabsorption by the device structure. The reverse bias conditions of theanode terminal electrode (parts 533A, 533B) and the cathode terminalelectrode (parts 531A, 531B) are configured such the diode detectorproduces photocurrent between the anode terminal electrode (parts 533A,533B) and the cathode terminal electrode (parts 531A, 531B) that isproportional to the intensity of the optical mode signal 504 absorbed bythe device structure. The photocurrent flows between the anode terminalelectrode (parts 533A, 533B) and cathode terminal electrode (parts 531A,531B) under the reverse bias. The current-blocking ion implant regions525A, 525B substantially reduces dark leakage current, which can greatlyreduce the sensitivity of the device if not addressed.

Electrical signals can be supplied to the first control electrode 581and the second control electrode 583 of the coupling section 503 inorder to change the coupling coefficient of the evanescent couplingbetween the waveguide 502 of the coupling section 503 and the straightsection 511 of the coupling waveguide 509. Specifically, the couplingcoefficient of the evanescent-wave coupling between the two waveguidescan be changed (i.e., modulated) by controlling the amount of charge(holes) that fills the QW(s) of the p-type modulation doped QW structure20 for the waveguide 502 of the coupling section 503, which dictates theshifting of the absorption edge and index of refraction of the QW(s) ofthe p-type modulation doped QW structure 20 for the waveguide 502 of thecoupling section 503. Charge can be added to (or removed from) the QW(s)of the p-type modulation doped QW structure 20 by a suitable biascurrent source and/or bias current sink that is electrically coupled tothe first control electrode 581. The second control electrode 883 tiedto ground potential. For continuous output or input, a DC electricalsignal can be supplied to the first control electrode 581 and the secondcontrol electrode 583 in order to activate and deactivate the evanescentcoupling between the waveguide 502 and the straight section 511 of thecoupling waveguide 509. Alternatively, a time-varying differentialelectrical signal can be supplied to the first control electrode 581 andthe second control electrode 583 in order to modulate the evanescentcoupling between the waveguide 502 and the straight section 511 of thecoupling waveguide 509. Such coupling modulation generates a modulatedoptical signal based upon the optical mode signal 504 that propagates inthe waveguide 502 of the resonator 501. The modulated optical signalpropagates through the straight section 511 of the coupling waveguide509 and is output therefrom. The modulated optical signal can have anoptical OOK modulation format (i.e., digital pulsed-mode optical signal)or possibly a higher order optical modulation format (such as opticaldifferential phase shift keying format or optical differentialquadrature phase shift keying format).

Electrical signals can be supplied to the first tuning electrode (parts571A, 571B) and the second tuning electrode (parts 573A, 573B) of thetuning portion 507 of section 503D in order to tune the characteristicwavelength λ_(D) of the optical mode signal 504 that propagates in thewaveguide 502. Specifically, the bias signal between the first tuningelectrode (parts 571A, 571B) and the second tuning electrode (parts573A, 573B) can populate the QW(s) of the p-type modulation doped QWstructure 20 with holes, which shifts the absorption edge to shorterwavelengths and thus induces a significant index change. The indexchange can modify the length of the optical path of the waveguide 502and therefore change the characteristic wavelength λ_(D) of the opticalmode signal 504 that propagates in the waveguide 502.

In alternate embodiments, the active portions of the resonator 501(i.e., sections 505A, 505B, 503B, and 503C) can be configured withmesas, contact implants and metallization for electrical contact to toplayer 30 for an anode terminal electrode (or parts thereof) andelectrical contact to the n-type modulation doped QW structure 24 for acathode terminal electrode or parts thereof. In this configuration, theactive portions of the resonator 501 (i.e., sections 505A, 505B, 503B,and 503C) can operate as a top diode laser or top diode detector asdescribed herein. Similarly, the coupling section 503C of the resonator501 can be configured with mesas, contact implants and metallization forelectrical contact to top layer 30 for a first control terminalelectrode and electrical contact to the n-type modulation doped QWstructure 24 for a second control electrode that are used to control thecoupling coefficient of the evanescent-wave coupling between thewaveguide 502 of the coupling section 503 and the straight section 511of the coupling waveguide 509. Specifically, the coupling coefficient ofthe evanescent-wave coupling between two waveguides can be changed(i.e., modulated) by controlling the amount of charge (electrons) thatfills the QW(s) of the n-type modulation doped QW structure 24 for thewaveguide 502 of the coupling section 503, which dictates the shiftingof the absorption edge and index of refraction of the QW(s) of then-type modulation doped QW structure 24 for the waveguide 502 of thecoupling section 503. Similarly, the tuning section 507 of the resonator501 can be configured with mesas, contact implants and metallization forelectrical contact to top layer 30 for a first tuning electrode andelectrical contact to the n-type modulation doped QW structure 24 for asecond tuning electrode that are used to tune the characteristicwavelength λ_(D) of the optical mode signal 504 that propagates in thewaveguide 502. Specifically, the characteristic wavelength λ_(D) of theoptical mode signal 504 can be changed (i.e., modulated) by controllingthe amount of charge (electrons) that fills the QW(s) of the n-typemodulation doped QW structure 24 for the waveguide 502 of the tuningsection 507, which dictates the shifting of the absorption edge andindex of refraction of the QW(s) of the n-type modulation doped QWstructure 24 for the tuning section 507 of the waveguide 502 and theoptical path length of the waveguide 502 of the resonator.

In yet other embodiments, the active portions of the resonator 501(i.e., sections 505A, 505B, 503B, and 503C) can be configured withmesas, contact implants and metallization for electrical contact to toplayer 30 for an anode terminal electrode (or parts thereof) as well aselectrical contact to the n-type modulation doped QW structure 24 for ann-channel injector terminal electrode or parts thereof as well aselectrical contact to the p-type modulation doped QW structure 20 for ap-channel injector terminal electrode or parts thereof as well aselectrical contact to the bottom n-type contact layer 14 for a cathodeterminal electrode or parts thereof. In this configuration, the activeportions of the resonator 501 (i.e., sections 505A, 505B, 503B, and503C) can operate as a thyristor laser or thyristor detector asdescribed herein. Similarly, the coupling section 503C of the resonator501 can be configured with mesas, contact implants and metallization forelectrical contact to top layer 30, to the n-type modulation doped QWstructure 24, to the p-type modulation doped QW structure 20, and to thebottom n-type contact layer 14 for control terminal electrodes that areused to control the coupling coefficient of the evanescent-wave couplingbetween the waveguide 502 of the coupling section 503 and the straightsection 511 of the coupling waveguide 509. Specifically, the couplingcoefficient of the evanescent-wave coupling between two waveguides canbe changed (i.e., modulated) by controlling the amount of charge thatfills the QW(s) of the n-type modulation doped QW structure 24 and/orQW(s) of the p-type modulation doped QW structure 20 for the waveguide502 of the coupling section 503, which dictates the shifting of theabsorption edge and index of refraction of the QW(s) of the n-type orp-type modulation doped QW structures for the waveguide 502 of thecoupling section 503. Similarly, the tuning section 507 of the resonator501 can be configured with mesas, contact implants and metallization forelectrical contact to top layer 30, to the n-type modulation doped QWstructure 24, to the p-type modulation doped QW structure 20, and to thebottom n-type contact layer 14 for tuning electrodes that are used totune the characteristic wavelength λ_(D) of the optical mode signal 504that propagates in the waveguide 502. Specifically, the characteristicwavelength λ_(D) of the optical mode signal 504 that propagates in thewaveguide 502 can be changed (i.e., modulated) by controlling the amountof charge that fills the QW(s) of the n-type modulation doped QWstructure 24 and/or QW(s) of the p-type modulation doped QW structure 20for the waveguide 502 of the tuning section 507, which dictates theshifting of the absorption edge and index of refraction of the QW(s) ofthe n-type or p-type modulation doped QW structures for the waveguide502 of the tuning section 507 and the optical path length of thewaveguide 502 of the resonator.

In alternate embodiments, the tuning section 507 can be realized as partof any one of the other optical resonator structures as described hereinin order to provide tunability of the wavelength of the optical modeprocessed by the optical resonator structure.

FIGS. 5F-5H illustrate a configuration of a closed-loop (rectangularpath) microresonator 500′ that includes a resonator 501′ andelectrically-controlled tuning reflector 591 that are realized as partof an optoelectronic integrated circuit that employs the layer structureof FIG. 1. The resonator 501′ is spaced from a section of a zig-zagwaveguide structure 509′ by a gap region. The zig-zag waveguidestructure 509′ is optically coupled to the resonator 501′ byevanescent-wave coupling over the gap region. Similar to the resonator501 of the embodiment of FIGS. 5A-5E as described above, the resonator501′ defines an active waveguide 502′ that follows a closed path that isgenerally rectangular in shape. The optical path length of the activewaveguide 502′ is tuned to the particular wavelength of the optical modesignal that is to propagate in the waveguide 502′. However, the tuningsection and isolating passive waveguide sections of the waveguide 502 ofthe embodiment of FIGS. 5A-5E is omitted and replaced with an activesection similar to the section 503C of FIG. 5B. Moreover, wavelengthtuning functionality is carried out by the tuning reflector 591 that isformed as part of the coupling waveguide 509.

In this embodiment, the active waveguide 502′ of the resonator 501′ isconfigured with mesas, contact implants and metallization for electricalcontact to top layer 30 for an anode terminal electrode (or partsthereof) and electrical contact to the n-type modulation doped QWstructure 24 for a cathode terminal electrode or parts thereof. Acollector terminal can be in electrical contact to the p-type modulationdoped QW structure 20 if desired. In this configuration, the activewaveguide 502′ of the resonator 501′ can operate as a top diode laser ortop diode detector as described herein. Similarly, the coupling sectionof the resonator 501′ can be configured with mesas, contact implants andmetallization for electrical contact to top layer 30 for a first controlterminal electrode and electrical contact to the n-type modulation dopedQW structure 24 for a second control electrode that are used to controlthe coupling coefficient of the evanescent-wave coupling between thewaveguide 502′ of the coupling section and the straight section of thecoupling waveguide 509′ as described herein.

In principle, the resonator 501′ produces light that propagates in boththe clockwise and counterclockwise sense along the optical path of thewaveguide 502′ of the resonator 501′ as indicted by the two sets ofarrows in FIG. 5F. Moreover, the evanescent coupling between thecoupling section of the resonator 501′ and the straight section of thecoupling waveguide 509′ operates on both clockwise and counterclockwiselight propagation within the resonator 501′. Specifically, the lightpropagating clockwise within the resonator 501′ is coupled to thecoupling waveguide 509′ to produce light that propagates in the couplingwaveguide 509′ toward the right side of FIG. 5F, and light propagatingcounterclockwise within the resonator 501′ is coupled to the couplingwaveguide 509′ to produce light that propagates in the couplingwaveguide 509′ toward the left side of FIG. 5F.

Similarly, the evanescent coupling between the straight section of thecoupling waveguide 509′ and the coupling section of the resonator 501′operates on both directions of light propagation within the couplingwaveguide 509′. Specifically, light propagating in the straight sectionof the coupling waveguide toward the right side of FIG. 5F is coupled tothe resonator 501′ to produce light that propagates clockwise in theresonator 501′, and light propagating in the straight section of thecoupling waveguide toward the left side of FIG. 5F is coupled to theresonator 501′ to produce light that propagates counterclockwise in theresonator 501′.

The tuning reflector 591 is a linear active waveguide device formed as areflector that builds upon the multiple directions of light propagationin the resonator 501′ as well as the multiple directions of evanescentcoupling provided between the straight section of the coupling waveguide509′ and the coupling section of the resonator 501′. The tuningreflector 591 has Bragg grating (such as a first-order or third-orderBragg grating) defined throughout the length of the active waveguidedevice. The Bragg grating can be defined by etching into the top layers(such as layers 26, 28, 30 of layer structure of FIG. 1) as shown inFIG. 5G. The Bragg grating operates to reflect any optical modes exitingthe straight section of coupling waveguide 509 in the direction of thetuning reflector 591 where the wavelength of such optical modescoincides with the Bragg frequency of the Bragg grating. All opticalmodes at other wavelengths will be passed through the tuning reflector591 or be absorbed.

For laser operations, the resonator 501′ produces optical mode(s) thatpropagate counter-clockwise within the waveguide 502′ of the resonator501′, which are coupled into the coupling waveguide 509′ to produceoptical mode(s) that propagate in the coupling waveguide 509′ to thetuning reflector 591. The incident optical mode(s) at wavelengths thatcoincide with the Bragg frequency of the Bragg grating of the tuningreflector 591 are reflected back and propagate in the reverse directionwithin the coupling waveguide 509′ where the mode is coupled into theresonator 501′ to produce optical mode(s) that propagates clockwise inthe resonator 501′ and generate more stimulated emission. This operationis repeated many times such that the wavelength of dominant optical modethat propagates in the resonator 501 corresponds to the Bragg frequencyof the Bragg grating. Such dominant optical mode propagating clockwisein the resonator 501 is coupled to the coupling waveguide 509 to producean output optical signal (which propagates in the direction away fromthe tuning reflector 591 and labeled “desired output direction” in FIG.5F). In this manner, optical modes that coincide with the Braggfrequency of the Bragg grating of the tuning reflector 591 make doublepasses through the resonator 501′ for improved stimulated emission. Thisoperation is repeated such that the wavelength of the dominant orprimary optical mode that propagates in the resonator 501′ correspondsto the Bragg frequency of the Bragg grating. With this operation, thedominant or primary optical mode that propagates in the resonator 501′is output from the coupling waveguide 509′, while optical modes that donot coincide with the Bragg frequency of the Bragg grating of the tuningreflector 591 are removed from the output signal by the operation of thetuning reflector 591.

For optical detection operations, the input optical signal is suppliedto the coupling waveguide 509′ from the end opposite the tuningreflector 591. Such input optical signal is coupled into the resonator501′ to produce optical mode(s) that propagate counter-clockwise withinthe waveguide 502′ of the resonator 501′ for absorption. Somecounter-clockwise propagating optical modes that are not absorbed can becoupled into the coupling waveguide 509′ to produce optical mode(s) thatpropagate in the coupling waveguide 509′ to the tuning reflector 591.The incident optical mode(s) with wavelengths that coincide with theBragg frequency of the Bragg grating of the tuning reflector 591 arereflected back and propagate in the reverse direction within thecoupling waveguide 509′ where the mode is coupled into the resonator501′ to produce optical mode(s) that propagate clockwise in theresonator 501′ for additional absorption. In this manner, optical modesthat coincide with the Bragg frequency of the Bragg grating of thetuning reflector 591 make double passes through the resonator 501′. Thisoperation is repeated such that the wavelength of the dominant orprimary optical mode that propagates in the resonator 501′ correspondsto the Bragg frequency of the Bragg grating.

For both laser operations and optical detection operations, the Bragggrating functions as a narrow-band filter where the Bragg frequency ofgrating that dictates the wavelength of the dominant or primary opticalmode that propagates in the resonator 501′. Such narrow-band filteringis useful for larger closed-loop resonators where the natural moderesonances are closely spaced from one another and thus do not provide anarrow wavelength band for the optical mode that propagates in theclosed-loop resonator.

The Bragg frequency of the Bragg grating of the tuning reflector 591 canbe electronically-controlled (or tuned) by controlled injection ofcharge that modifies the index of the region n2 of the Bragg grating asnoted in FIG. 5L. The charge injection can be controlled by travelingwave surface electrode parts 592A, 592B that are formed on the topsurface 30 on opposite sides of the Bragg grating along the length ofthe device as shown in FIG. 5G. Ion implanted source regions 593A and593B are also formed on opposite sides of the Bragg grating along thelength of the device and in contact with the n-type modulation doped QWstructure 24 of the device. Waveguide implants 594A, 594B can be formedon opposite sides of the Bragg grating at or near the same depth of theBragg grating along the length of the device as shown. Intermediateelectrode parts 595A, 595B are formed in contact with the ion implantedsource regions 593A and 593B. The traveling wave surface electrode parts592A, 592B form a CPW (Coplanar Waveguide) traveling wave transmissionline which is ideal to implement high speed tunability. A collectorterminal electrode 596 can be formed on an ion implant region 597 thatcontacts the p-type modulation doped interface 20 of the devicestructure. A top mirror can be formed over the device structure as shownin FIG. 5H. The CPW defined by traveling wave surface electrode parts592A, 592B can be terminated in its characteristic impedance Z_(o), andthe intermediate electrode parts 595A, 595B can be coupled to groundpotential as noted in FIG. 5F. Charge injection that modulates the indexn2 can be controlled by applying a traveling wave electrical RF signalto the CPW, and the Bragg grating frequency corresponding to the timedependent index n2 value can be obtained. Because the tuning is achievedby charge injection into the QW(s) of the n-type modulation doped QWstructure 24 of the device, the collector bias can change the voltage atwhich this happens similar to the threshold voltage of an HFET.Therefore the voltage window for tuning can be adjusted for the range ofinput signal. Note that for a 1st and 3rd order gratings, the reflectedwavelength λ_(o) and grating pitch Λ are related by Λ=λ_(o)/2 n _(eff)and Λ=3λ_(o)/2 n _(eff), respectively where n _(eff) is some function ofthe index n1 and the index n2 such as n _(eff)=(n1+n2)/2. The electricaltraveling wave will have a velocity of c=c_(o)/n_(elec) where _(co) isthe velocity of light and n_(elec) is effective index for the electricalwave, which is another function of n1 and n2 and the spacing between thetraveling wave surface electrode parts 592A, 592B.

Moreover, if the electrical velocity on the CPW (i.e., the rate at whichthe RF signal supplied to the CPW advances on the transmission line andgiven by c=c_(o)/n_(elec)) and the optical velocity (the rate at whichthe optical signal advances in the optical waveguide of the tuningreflector 591, which is bounded at the top by the Bragg grating, andgiven by=c_(o)/ n _(eff)) match one another (which is achieved when n_(eff)=n_(elec)), the maximum change of index n2 for a given chargeinjection level will be obtained.

Advantageously, the closed-loop microresonator 500′ of FIGS. 5F-5G canbe configured to provide the functionality equivalent to a tunable DFBlaser with higher speed, wider tunability, and a wider variety ofelectronic integration than is currently not possible instate-of-the-art technology.

In alternate embodiments, the tuning reflector 591 can be realized aspart of the coupling waveguide structure in conjunction with any one ofthe other optical resonator structures as described herein in order toprovide tunability of the wavelength of the optical mode processed bythe optical resonator structure.

FIGS. 6A-6C illustrate a split-electrode vertical cavity surfaceemitting device 600 realized as part of an optoelectronic integratedcircuit that employs the layer structure of FIG. 1. The device 600 canlogically be partitioned into two parts, a left half 601 and a righthalf 602 that each have a generally half-circular top profile as shownin FIG. 6A. A top mesa 612 extends across both the left half 601 and theright half 603 as best shown in FIG. 6B. A first intermediate mesa 618is defined on the left side 601 outside the outer periphery of the topmesa 612. The first intermediate mesa 618 is formed above (but near) then-type modulation doped QW structure 24. A second intermediate mesa 620is defined on the right side 603 outside the outer periphery of top mesa612 and opposite the first intermediate mesa 618. The secondintermediate mesa 620 is formed above (but near) the p-type modulationdoped QW structure 20. A bottom mesa 622 is defined by the n-type layer14 outside the periphery of both the first intermediate mesa 618 and thesecond intermediate mesa 620 and extends across both the left half 601and the right half 603 as best shown in FIG. 6B.

The top mesa 612 is formed by the top surface of layer 30 of the layerstructure of FIG. 1. An ion implant region 616 (preferably of n-typeions) can be implanted through the top mesa 612 to a depth within theone or more the top p-type layers 28, 30 on the left half 601 of thedevice. The ion implant region 616 can have a half-circle profile thatprovides a current barrier that funnels current injected from the anodeterminal electrode 614 into the active region 650 defined by the righthalf 602 of the device as illustrated by arrow 651 in FIG. 6B.

The anode terminal electrode 614 is formed on the top mesa 612 with ahalf-circle pattern as best shown in FIG. 6A. The anode terminalelectrode 614 contacts the top p-type ohmic contact layer 30. The metalof the anode terminal electrode 614 can be tungsten or other suitablemetal or alloy. The metal of the anode terminal electrode 614 as well asthe implant region 616 can be formed by a lift off by oxide process asdescribed below with respect to FIGS. 9A-9D.

The first intermediate mesa 618 is formed by patterning and etching thelayer structure to a depth in layer(s) 26 above (but near) the n-typemodulation doped quantum well structure 24 to define the sidewall thatforms the half-circle profile of the mesa 618 for the left half 601 ofthe device as evident from FIG. 6A. The patterned metal of the anodeterminal electrode 614 can be used as a mask layer for the etch of thissidewall if desired.

The second intermediate mesa 620 is formed by patterning and etching thelayer structure to a depth in spacer layer(s) 22 above (but near) thep-type modulation doped quantum well structure 20 to define the sidewallthat forms the half-circle profile of the mesa 620 for the right half602 of the device as evident from FIG. 6A.

An ion implant region 624 is defined by ion implantation of n-type ionsthrough the first intermediate mesa 618. The ion implant 624 isimplanted to a depth that encompasses the n-type modulation doped QWstructure 24 with the half-circle pattern that is disposed laterallyoutside the projection of the sidewall that leads to the firstintermediate mesa. The implant region 624 provides for electricalcontact to the annular n-type modulation doped QW structure 24 of thetwo halves 601, 602 of the device.

An ion implant region 626 is defined by ion implantation of p-type ionsthrough the second intermediate mesa 620. The implant region 626provides for electrical contact to the annular p-type modulation dopedQW structure 20 of the two halves 601, 602 of the device. A rapidthermal anneal (RTA) oxide can be deposited on the resultant structureand RTA operations are carried out to activate the implant regions 624and 626 as desired. The ion implant region 626 is similar to the ionimplant region 719 of the p-channel HFET as described above with respectto FIG. 7 and can be implanted together with this implants with the samep-type acceptor ions species and annealed as described above.

High resistance deep oxygen ion implant regions 628A and 628B are thenimplanted in the bottom n+ contact layer 14 through the intermediatemesas 618 and 620 for the left and right halves 601 and 602 of thedevice, where such high resistance effectively blocks current flowtherethrough. The oxygen ion implant regions 628A and 628B form a nearcomplete circle with a gap 630 that is devoid of the current blockingoxygen ions. An RTA is then performed in order to activate the oxygenion implant regions 628A, 628B. The ion implant regions 628A, 628B issimilar to the ion implant region 721 of the p-channel HFET as describedabove with respect to FIG. 7 and can be implanted together and annealedas described above.

The resultant structure is patterned and etched to form the annularsidewalls that extends downward to the bottom mesa 622 formed in thebottom ohmic contact layer 14. The bottom mesa 622 has a circularprofile outside the periphery of the first intermediate mesa 618 and thesecond intermediate mesa 620 for the left and right halves 601, 602 ofthe device.

An n-channel injector terminal electrode 632 is formed on the firstintermediate mesa 618 of the left half 601 with a half-circle pattern asbest shown in FIGS. 6A and 6B. The n-channel injector terminal electrode632 contacts the n-type ion implant region 624, which contacts then-type modulation doped QW structure 24 of the device structure. Ap-channel injector terminal electrode 634 is formed on the secondintermediate mesa 620 of the right half 602 with a half-circle patternas best shown in FIGS. 6A and 6B. The p-channel injector terminalelectrode 634 contacts the p-type ion implant region 626, which contactsthe p-type modulation doped QW structure 20 of the device structure. Thegap 630 of the oxygen implant region is positioned adjacent a cathodeterminal electrode 636 (which is preferably shaped as a small tab) thatis formed on a portion of the bottom mesa 622 adjacent the gap 630 asevident from the FIGS. 6A and 6C. The gap 630 provides a narrow pathwayfor current flow from the active region 650 to the cathode terminalelectrode 636 as evident from FIG. 6C. Similar to the source, drain,gate and collector terminal electrodes of the p-channel HFET device asdescribed above with respect to FIGS. 7A and 7B, the metal of thep-channel injector terminal electrode 634 is preferably an Au—Be alloy,and the metal of the n-channel injector terminal 632 and the cathodeterminal electrode 636 is preferably an Au—Ge—Ni alloy. The resultantstructure can be heated to treat the metal alloys of the electrodes ofthe device as desired. Such metallization can be carried out in tandemwith the metallization of the source, drain and gate electrodes of thep-channel HFET device as described above with respect to FIGS. 7A and 7Bor the electrode(s) of other devices integrally formed on the substrate10.

Following the metallization, a trench etch can expose the bottom mirrorlayers 12. The exposed bottom mirror layers 12 can be oxidized in steamambient. A top mirror (not shown) can cover the mesas 612, 618, 620 andthe sidewalls of the device 600, if desired. The index changes providedby the top mesa 612 (together with the top mirror when present), thesidewalls of the right half 601, the current blocking implant 616, andthe bottom DBR mirror 12 form a resonant cavity of a vertical cavitylaser emitter or detector. The top surface of the mesa 612 of the righthalf 602 (which is left open and not covered by the anode metal 614)defines an aperture that leads to the active region 650 of this verticalcavity. Electrically, the vertical cavity thyristor device 500 canoperate as an electrically-pumped thyristor laser or thyristor detector.

For the thyristor laser, the device structure switches from anon-conducting/OFF state (where the current I through the device issubstantially zero) to a conducting/ON state (where current I issubstantially greater than zero) when i) the anode terminal electrode614 is forward biased with respect to the cathode terminal electrode 636and ii) the voltage between n-channel injector 632 and the anodeelectrode 614 is biased such that charge is produced in the n-typemodulation doped QW structure 24 that is greater than the criticalswitching charge Q_(CR), which is that charge that reduces the forwardbreakdown voltage such that no off state bias point exists. The voltagebetween p-channel injector electrode 634 and the cathode electrode 636can also be configured to produce a charge in the p-type modulationdoped QW structure 20 that is greater than the critical switching chargeQ_(CR). The critical switching charge Q_(CR) is unique to the geometriesand doping levels of the device. The device switches from theconducting/ON state (where the current I is substantially greater thanzero) to a non-conducting/OFF state (where current I is substantiallyzero) when the current I through device falls below the hold current ofthe device for a sufficient period of time such that the charge in then-type modulation doped QW structure 24 (or the charge in the p-typemodulation doped QW structure 20) decreases below the holding chargeQ_(H), which is the critical value of the channel charge which willsustain holding action. Thus, if the anode terminal 614 is forwardbiased with respect to the cathode terminal 636 and the n-channelinjector terminal 632 (and/or the p-channel injector terminal 634) isbiased to produce the critical switching charge Q_(CR) in the n-typemodulation doped QW structure 24 (or in the p-type modulation doped QWstructure 20), then the device will switch to its conducting/ON state.If the current I in the conducting/ON state is above the threshold forlasing I_(TH), then photon emission will occur within the devicestructure. For the vertical cavity thyristor device 600, such photonemission produces an optical signal that exits through the aperture inthe top mesa 612 for output therefrom. The current-blocking oxygen ionimplant regions 628A, 628B funnels the current that flows from betweenthe anode terminal electrode 614 and the cathode terminal electrode 636into the QW channel of the p-type modulation doped QW structure 20within the vertical resonant cavity of the device. Such currentfunneling enhances the current density of the injected current in the QWchannel of the p-type modulation doped QW structure 20 within thevertical resonant cavity of the device, which can improve the outputpower of the device and/or lower the laser threshold voltage of thedevice.

For the thyristor detector, an input optical signal is injected throughthe aperture in the top mesa 612 into the vertical cavity of the devicefor absorption by the device structure. The device structure switchesfrom a non-conducting/OFF state (where the current I through the deviceis substantially zero) to a conducting/ON state (where current I issubstantially greater than zero) in response to the optical signalproducing charge in the n-type modulation doped QW structure 24 and/orthe p-type modulation doped QW structure 20 resulting from photonabsorption of the optical signal. Specifically, the anode terminalelectrode 614 is forward biased with respect to the cathode terminalelectrode 636 and the voltage between n-channel injector 632 and theanode electrode 614 (and/or the voltage between the p-channel injector634 and the cathode terminal electrode 636) is biased such that thatcharged produced in the n-type modulation doped QW structure 24 (and/orthe p-type modulation doped QW structure 20) resulting from photonabsorption of the whispering gallery mode optical signal is greater thanthe critical switching charge Q_(CR). When the whispering gallery modeoptical signal is removed, the device switches from the conducting/ONstate (where the current I is substantially greater than zero) to anon-conducting/OFF state (where current I is substantially zero) whenthe charge in the n-type modulation doped QW structure 24 (and/or thep-type modulation doped QW structure 20) decreases below the holdingcharge Q_(H).

For both the thyristor laser and the thyristor detector, thecurrent-blocking ion implant regions 628A, 628B reduces the capacitancebetween the p-channel injector terminal electrode 634 and the cathodeterminal electrode 636 of the device. This capacitance can drasticallylower the speed of response of the device if not reduced.

FIGS. 8A to 8C illustrate a dual-wavelength hybrid device 800 realizedas part of an optoelectronic integrated circuit that employs the layerstructure of FIG. 1. The dual-wavelength hybrid device 800 is a hybridof two parts: a central part that operates as a vertical cavity deviceat a first wavelength corresponding to the material of the n-typemodulation doped QW structure 24, and an outside part that operates as awhispering gallery mode device at a second wavelength corresponding tothe material of the p-type modulation doped structure 20. The device 800includes a top mesa 812 with an annular shallow trench that forms afirst intermediate mesa 814. A bottom mesa 824 is defined outside theouter periphery of the second intermediate mesa 822.

The top mesa 812 is formed by the top surface of layer 30 of the layerstructure of FIG. 1. A split anode terminal electrode with twoconcentric annular parts 818A, 818B is formed on the top mesa 812 asbest shown in FIGS. 8A and 8B. The anode terminal electrode parts 818A,818B both contact the top p-type ohmic contact layer 30. The metal ofthe anode terminal electrode parts 818A, 818B can be tungsten or othersuitable metal or alloy.

Two ion implant regions 820A, 820B (preferably of n-type ions) can beimplanted through the top mesa 812 to a depth within the top layers 26,28, 30. The ion implant regions 820A, 820B can have concentric circularprofiles that provide current barriers that funnel current injected fromthe anode terminal electrode parts 818A, 818B into both central andperipheral active regions of the device. The metal of the anode terminalelectrode parts 818A, 818B as well as the ion implant regions 820A, 820Bcan be patterned by a lift off by oxide process as described below withrespect to FIGS. 9A-9D.

The shallow trench that defines the first intermediate mesa 814 isdisposed between the two anode terminal electrode parts 818A, 818B andcan formed by patterning and etching the layer structure to a depth inlayer(s) 26 above (but near) the n-type modulation doped quantum wellstructure 24. The first intermediate mesa 814 has an annular profilethat is concentrically located between the two anode terminal electrodeparts 818A, 818B. The patterned metal of the two anode terminalelectrode parts 818A, 818B can be used as a mask layer for the etch ofthis shallow trench if desired.

The second intermediate mesa 822 is formed by patterning and etching thelayer structure to a depth in spacer layer(s) 22 above (but near) thep-type modulation doped quantum well structure 20 as evident from FIG.8B. The second intermediate mesa 822 is defined by an annular sidewall817-1 that extends down from the outer periphery of the top mesa 812 asshown in FIGS. 8B and 8C. The second intermediate mesa 822 has agenerally annular profile that extends laterally outside the outerperiphery of the top mesa 812 as evident from FIGS. 8A and 8B. Thepatterned metal of the outside anode terminal electrode part 818B can beused as a mask layer for the etch of the sidewall 817-1 if desired. Theoutside current blocking implant region 820 can be offset laterally fromthe sidewall 817-1 as evident from FIG. 8B.

The patterning and etching of the sidewall 817-1 can also define twoopposed sidewalls 817-2 and 817-3 of a waveguide rib that defines acoupling waveguide 838 extending tangential to the outer annularsidewall 817-1 of the device 800 as best shown on FIG. 8A. The sidewall817-2 of the coupling waveguide 838 is offset from the annular sidewall817-1 by a narrow gap 840 and the height of the coupling waveguide 838can match the height of the top mesa 812 of the device 400 as best shownin FIG. 8C.

An ion implant region 825 is defined by ion implantation of n-type ionsthrough the first intermediate mesa 814. The ion implant 825 isimplanted to a depth that encompasses the n-type modulation doped QWstructure 24 with an annular pattern that is disposed laterally withinthe projections of the annular sidewalls of the shallow top trench asevident from FIG. 8B. The implant region 825 provides for electricalcontact to the annular n-type modulation doped QW structure 24 thatsurrounds the implant region 825 on both sides of the implant region825.

Two ion implant regions 828, 830 are defined by ion implantation throughthe second intermediate mesa 822. The ion implant regions 828, 830 aresimilar to the ion implant regions 719 and 721 of the p-channel HFET asdescribed above with respect to FIG. 7 and can be implanted togetherwith these implants with the same ions species (p-type acceptor ions forthe implant region 828 and oxygen ions for the implant regions 830) andannealed as described above. The implant region 828 is implanted to adepth that encompasses the p-type modulation doped QW structure 20 withan annular pattern that is disposed laterally outside the projection ofthe annular sidewall that extends downward to the second intermediatemesa 822 as evident from FIG. 8B. The implant region 828 provides forelectrical contact to the annular p-type modulation doped QW structure20 that is surrounded by the implant region 828. The ion implant region830 (which has the deepest depth of the two implant regions) isimplanted into the N+-type layer 14 with a pattern that is disposedlaterally outside the projection of the annular sidewall that extendsdownward to the second intermediate mesa 822 as evident from FIG. 8B. Inthis manner, the implant region 828 overlies the implant region 830. Thehigh resistance deep oxygen ion implant region 830 effectively blockscurrent flow therethrough and thus operates to funnel or steer currentinto the active region of the resonant cavity of the device.Furthermore, the current blocking oxygen ion implant region 820 definesan isolation region between the p-type implant region 828 and the bottomN+-type ohmic contact layer 14 of the layer structure. Such isolationregion is substantially devoid of conducting species and significantlyreduces the capacitance between the p-channel injector terminalelectrode 834 and the cathode terminal electrode 836 of the device. Thiscapacitance can drastically lower the speed of response of the device ifnot reduced.

The resultant structure is patterned and etched to form a generallyannular sidewall that extends downward to the bottom mesa 824 formed inthe bottom ohmic contact layer 14. The bottom mesa 824 has a generallycircular profile outside the periphery of the second intermediate mesa822 as shown in FIG. 8A.

An n-channel injector terminal electrode 816 is formed on the firstintermediate mesa 814 with an annular pattern as best shown in FIGS. 8Aand 8B. The n-channel injector terminal electrode 816 contacts then-type ion implant region 825, which contacts the n-type modulationdoped QW structure 24 of the device structure. A p-channel injectorterminal electrode 834 is formed on the second intermediate mesa 822with a generally annular pattern as best shown in FIGS. 8A and 8B. Thep-channel injector terminal electrode 834 contacts the p-type ionimplant region 828, which contacts the p-type modulation doped QWstructure 20 of the device structure. The gap 832 in the deep oxygen ionimplant region 830 is positioned adjacent a cathode terminal electrode836 (which is preferably shaped as a small tab) that is formed on aportion of the bottom mesa 824 adjacent the gap 832 as evident from theFIGS. 8A and 8C. The gap 832 provides a narrow pathway for current flowfrom the central and peripheral active regions to the cathode terminalelectrode 836 as evident from FIG. 8C. Similar to the source, drain,gate and collector terminal electrodes of the p-channel HFET device asdescribed above with respect to FIGS. 7A and 7B, the metal of thep-channel injector terminal electrode 834 is preferably an Au—Be alloy,and the metal of the n-channel injector terminal 832 and the cathodeterminal electrode 836 is preferably an Au—Ge—Ni alloy. The resultantstructure can be heated to treat the metal alloys of the electrodes ofthe device as desired. Such metallization can be carried out in tandemwith the metallization of the source, drain and gate electrodes of thep-channel HFET device as described above with respect to FIGS. 7A and 7Bor the electrode(s) of other devices integrally formed on the substrate10.

Following the metallization, a trench etch can expose the bottom mirrorlayers 12. The exposed bottom mirror layers 12 can be oxidized in steamambient. A dielectric top mirror (not shown) can cover the mesas 812,822, 824 and the sidewalls of the device 800, if desired. The dielectricmaterial of the top mirror can fill the gap 840.

The index changes provided by the top mesa 812 (together with the topmirror when present and the bottom DBR mirror 12 in the central regionof the device and possible other parts of the device form a resonantcavity of a thyristor vertical cavity laser emitter or detector. The topsurface of the mesa 812 in the central region of the device (which isleft open and not covered by the anode metal portions 818A, 818B)defines an aperture that leads to the central active region of thisvertical cavity. Furthermore, the index changes provided by the top mesa812 (together with the top mirror when present), the sidewall 817-1 ofthe device, the implants 820B, 826, 828, and the bottom DBR mirror 12 inthe periphery of the device form a resonant cavity having an annularvolume that supports propagation of a whispering gallery mode. Thethickness of the disk-shaped annular volume can be configured tocorrespond to at or near one wavelength (for example, a thickness at ornear 1 μm for a whispering gallery optical mode signal in thenear-infrared range of the electromagnetic spectrum). The thickness ofthe disk-shaped annular volume can encompass relatively equal portionsof the layer structure of FIG. 1 above and below the p-type modulationdoped quantum well structure 20. The coupling waveguide 838 provides forevanescent coupling of light to and/or from the peripheral resonantcavity of the device 800 that supports propagation of a whisperinggallery mode.

The device 800 can be configured to perform a first optical modeconversion function where an in-plane optical signal (which is input tothe coupling waveguide 838) is converted to a vertical optical modesignal that is emitted from the central aperture of the device 800.Specifically, a whispering gallery mode is coupled into the peripheralresonant cavity from the coupling waveguide 838 by evanescent coupling.This whispering gallery mode propagates around the peripheral resonantcavity, where it is absorbed by the device structure. Such absorptionadds charge to the QW(s) of the n-type modulation doped QW structure 24(or to the P-type modulation doped structure 20) such that the channelcharge exceeds the critical switching charge Q_(CR), which turns thecentral thyristor vertical cavity device ON. The ON current isconfigured to produce a vertical cavity mode for output.

In one embodiment, the first optical mode conversion function can beconfigured to perform wavelength conversion where the in-plane opticalsignal input to the coupling waveguide 838 is at a first wavelength λ₁(e.g., 980 nm), and the vertical mode emitted from the central activeregion of the device 800 is at a second wavelength λ₂ (e.g., 1310 nm).In this embodiment, the p-type modulation doped QW structure 20 caninclude one or more QD layers that are configured to absorb at the firstwavelength λ₁, and the n-type modulation doped QW structure 24 caninclude one or more QD layers that are configured to emit at secondwavelength λ₂. The electrodes of the device are biased such that thethyristor action turns ON in response to detection of the whisperinggallery mode at the first wavelength λ₁ and turns OFF when thewhispering gallery mode at the first wavelength λ₁ is not present, andthe n-type modulation doped QW structure 24 with suitable QD layers emitat the second wavelength λ₂ when the thyristor action is ON.

The device 800 can also be configured to perform a second optical modeconversion function where a vertical optical mode is supplied to thedevice 800 and injected through the central aperture of the device 800and converted to an in-plane optical signal that is output from thecoupling waveguide 838. Specifically, a vertical optical mode issupplied to the device 800 and injected through the central aperture ofthe device 800 where it is absorbed by the device structure of thevertical resonant cavity. Such absorption adds charge to the QW(s) ofthe n-type modulation doped QW structure 24 (or to the P-type modulationdoped structure 20) such that the channel charge exceeds the criticalswitching charge Q_(CR), which turns the central thyristor verticalcavity device ON. The ON current is configured to produce a whisperinggallery mode in the peripheral resonant cavity, which is coupled to thecoupling waveguide 838 by evanescent coupling and produces the in-planeoptical signal for output.

In one embodiment, the second optical mode conversion function can beconfigured to perform wavelength conversion where vertical mode injectedinto the central active region of the device 800 is at a firstwavelength λ₁ (e.g., 1310 nm), and the in-plane optical signal output bythe coupling waveguide 838 is at a second wavelength λ₂ (e.g., 980 nm).In this embodiment, the n-type modulation doped QW structure 24 caninclude one or more QD layers that are configured to absorb at the firstwavelength λ₁, and the p-type modulation doped QW structure 20 caninclude one or more QD layers that are configured to emit at secondwavelength λ₂. The electrodes of the device are biased such that thethyristor action turns ON in response to detection of the verticalcavity mode at the first wavelength λ₁ and turns OFF when the verticalcavity mode at the first wavelength λ₁ is not present, and the p-typemodulation doped QW structure 24 with suitable QD layers emit at thesecond wavelength λ₂ when the thyristor action is ON.

For both the thyristor laser and the thyristor detector, thecurrent-blocking ion implant regions 628A, 628B operate to funnel orsteer current into the active regions for the resonant cavities of thedevice, and also reduce the capacitance between the p-channel injectorterminal electrode 834 and the cathode terminal electrode 686 of thedevice. This capacitance can drastically lower the speed of response ofthe device if not reduced.

FIG. 9A to 9D illustrate exemplary fabrication steps that form dopantimplant regions that are self-aligned to patterned metal for an aperturethat is part of optoelectronic device realized in an integrated circuitwafer that employs the layer structure of FIG. 1. An aperture is formedat the top surface of the layer structure to allow for light to exit orenter into the active region of the device. Anode metal regions and/orimplant regions can be used to block light from exiting or entering intothe active region of the device structure and thus form the boundary ofthe aperture. In the steps of FIGS. 9A to 9D, a first mask is depositedand patterned on the top surface 901 of layer 30 of the layer structureof FIG. 1. In the one embodiment, the first mask comprises a dual layerstructure of oxide and nitride as shown. The mask preferably has athickness of 4000-5000 Å. The pattern of the mask defines a feature 901that protects the area of the aperture 905 that results from the processas shown in FIG. 9D.

Then, one or more implant regions (such as two implant regions 907A,907B as shown) are implanted into the layer structure outside the maskfeature 903. In one embodiment, the one or more implant regions (e.g.,regions 907A, 907B) are implanted to a depth that encompasses one ormore of the p-type layers 26 and 28 of the layer structure of FIG. 1. Inthis case, the implant regions) employ n-type species of sufficientdensity that convert the p-type implanted region to n-type and produce apn junction that blocks the flow of hole current flow verticallydownwards. This forces the hole current to flow laterally to theun-implanted active region of the device structure disposed below theaperture 905. In another, embodiment, the implant region(s) can beimplanted to a depth below the QW(s) of the n-type modulation doped QWstructure 24. This requires higher energy to place the implant regionsbelow such QW(s). In this case, the implant regions 907A, 907B operateto increase the “as grown” barrier to conduction of holes by theaddition of more n type doping near the modulation doping of the n-typemodulation doped QW structure 24. The larger barrier means that p-typeconduction over this barrier is reduced and so the hole current from thetop contact flows laterally where the barrier is lower (i.e., thevertically down conduction is blocked) preferentially to theun-implanted active region of the device structure disposed below theaperture 905. The ions species of the implant region(s) can be Si ionsdue to its lower mass and larger possible range. SiF ions may also beused. The advantage of locating the current blocking implant region(s)below the QW of the n-type modulation doped QW structure 24 is that thetop p-type layers 28 and 30 can be made thinner (preferably a ½λ abovethe QW), which makes it easier to fabricate HFETs with a lower profiletopology. Another advantage of this approach is a lower laser resistanceand therefore reduced heat generation in the laser active region whichis important for stable laser operation in the integrated environment.The implant region(s) can also provide for lateral confinement of lightwithin the active region of the device structure disposed below theaperture 905.

Next, the metal material 909 for the top surface electrode, which can betungsten or some other suitable metal or metal alloy, is deposited suchthat it covers the top surface 901 and the mask feature 903 as shown inFIG. 9B.

Next, a second mask 911 (preferably formed from photoresist material) isdeposited and patterned to define a window that overlies the maskfeature 903. The window is used as part of an etch operation that etchesthrough the window down through the metal 909 and the mask feature 901to a depth at or near the top surface 901 in the area that results inthe aperture 905. The window is smaller than the width of the maskfeature 901, and thus leaves behind one or more sidewalls (such as theopposed sidewalls 915A, 915B) of the mask feature 901. The sidewall(s)of the mask feature can have a width dimension on the order of 1-2 μm.This etch operation can employ an anisotropic etching process thatdefine a near vertical profile for the sidewall(s) of the mask feature.An example of a suitable anisotropic etching process is dry reactive ionetching employing SF6.

With the second mask 911 remaining in place or possibly removed, theresultant structure is etched in BOE (Buffered Oxide Etch). The BOEetches sideways and undercuts the sidewall(s) (e.g., sidewalls 915A,915B) of the mask feature 901 as well as the adjacent sidewall(s) of themetal material 909 and the overlying second mask 911 (if present) toform the resultant structure as shown in FIG. 9D. In this resultantstructure, the aperture 905 is formed between the opposed surfaceelectrode parts 909A, 909B. This procedure is designated lift-off byoxide.

Note that the current blocking implant(s) are disposed adjacent theaperture 905 below the corresponding surface electrode. Specifically,the opposed edge(s) of the implant region(s) are aligned laterally withthe opposed edges of the surface electrode that define the boundaries ofthe aperture. This self-aligned configuration of the implant region(s)and the surface electrode is advantageous because it can eliminate onemask procedure, aid in minimizing resistance of the top surface layers26, 28, 30 and aid in producing uniformity and higher yield over largeareas.

In alternate embodiments, the surface electrode that define theboundaries of the aperture can be patterned and etched away aftermetallizing all of the electrodes of the devices of the integratedcircuit and prior to depositing the dielectric material of the topmirror of such device, if used.

In yet other embodiments, the n-type and p-type doping characteristicsof the epitaxial layer of FIG. 1 can be reversed with respect to oneanother. In this configuration, the bottom layers 14′, 16′ have p-typedoping. The bottom layer 14′ provides a P+-type ohmic contact layer. Ann-type modulation doped quantum well structure 20′ can be formed abovethe bottom layers 14′, 16′. The n-type modulation doped structure 20′has a layer of N+-type modulation doping on the bottom side of thestructure 20′. A p-type modulation doped quantum well structure 24′ canbe formed above the n-type modulation doped structure 20′. The p-typemodulation doped structure 24′ has a layer of P+-type modulation dopingon the top side of the structure 24′. The top layers 26′, 30′ haven-type doping. The top layer 30′ provides an N+-type ohmic contactlayer.

In yet other embodiments, any one of the optical resonators as describedherein can be replicated to form an array of optical emitters ordetectors for parallel optical data links or wavelength divisionmultiplexed operations. Moreover, any one of the optical resonator andcoupling waveguide systems as described herein can be replicated andpositioned adjacent one another to provide for optical switchingfunctions between input and output waveguides and possibly other opticalfunctions as desired.

In still other embodiments, the devices as described herein can beformed from the device structure of FIG. 10, which includes a bottomdistributed Bragg reflector (DBR) mirror layers 1003 formed on substrate1001. The bottom DBR mirror layers 1003 are typically formed bydepositing pairs of semiconductor or dielectric materials with differentrefractive indices. When two materials with different refractive indicesare placed together to form a junction, light will be reflected at thejunction. The amount of light reflected at one such boundary is small.However, if multiple junctions/layer pairs are stacked periodically witheach layer having a quarter-wave (λ/4) optical thickness, thereflections from each of the boundaries will be added in phase toproduce a large amount of reflected light (e.g., a large reflectioncoefficient) at the particular center wavelength κ_(C). Deposited uponthe bottom DBR mirror layers 1003 is a metamorphic buffer 1005 thatsignificantly reduces strain due lattice mismatch between the overlyingactive device structure and the underlying bottom DMR mirror layers 1003and substrate 1001. Specifically, the metamorphic buffer 1005accommodates lattice mismatch between the underlying structure (bottomDBR mirror layers 1003 and substrate 1001) and the overlying structure(the alloys of the active device structure) and absorbs strain due tosuch lattice mismatch while minimizing the nucleation of dislocations.Deposited on the metamorphic buffer 1005 is one or more spacer layers1007 followed by an active device structure suitable for realizingcomplementary heterostructure field-effect transistor (HFET) devices.The first of these complementary HFET devices is a p-channel HFET whichhas a p-type modulation doped quantum well (QW) structure 1015 with ann-type gate region (i.e., bottom n-type ohmic contact layer(s) 1009 andbottom n-type region layer(s) 1011) below the p-type modulation doped QWstructure 1015. One or more spacer layers 1013 is disposed between thep-type modulation doped quantum well (QW) structure 1015 and theunderlying bottom n-type layer(s) 1011. One or more spacer/barrierlayers 1017 are disposed above the p-type modulation doped QW structure1015. A QD-In-QW structure 1019 is formed above the spacer/barrierlayer(s) 1017, where the QD-In-QW structure 1019 includes at least oneQW layer with self-assembled quantum dots (QDs) embedded therein. Thesecond of these complementary HFET devices is an n-channel HFET whichincludes an n-type modulation doped QW structure 1027 with a p-type gateregion (i.e., p-type ohmic contact layer(s) 1033 and p-type layer(s)1031) formed above the n-type modulation doped QW structure 1027. One ormore spacer layers 1029 is disposed between the n-type modulation dopedquantum well (QW) structure 1027 and the overlying p-type layer(s) 1031.One or more spacer/barrier layers 1025 are formed below the n-typemodulation doped quantum well (QW) structure 1027. A QD-In-QW structure1023 is formed below the spacer/barrier layer(s) 1025, where theQD-In-QW structure 1023 includes at least one QW layer withself-assembled quantum dots (QDs) embedded therein. One or more spacerlayer(s) 1021 are formed between the QD-In-QW structure 1019 and theQD-In-QW structure 1023. The layers encompassing the spacer layer(s)1021 and the n-type modulation doped QW structure 1027 forms thecollector region of the p-channel HFET. Similarly, the layersencompassing the spacer layer 1021 and the p-type modulation doped QWstructure 1015 forms the collector region of the n-channel HFET. Suchcollector regions are analogous to the substrate region of a MOSFETdevice as is well known. Therefore a non-inverted n-channel HFET deviceis stacked upon an inverted p-channel HFET device as part of the activedevice structure.

The active device layer structure begins with bottom n-type ohmiccontact layer(s) 1009 which enables the formation of ohmic contactsthereto. Deposited on layer(s) 1009 are one or more n-type layers 1011and one or more spacer layer(s) 1013 which serve electrically as part ofthe gate of the p-channel HFET device and optically as a part of thelower waveguide cladding of the device. Deposited on layer(s) 1013 isthe p-type modulation doped QW structure 1015 that defines a p-typecharge sheet offset from one or more QWs (which may be formed fromstrained or unstrained heterojunction materials) by an undoped spacerlayer. The p-type charge sheet is formed first below the undoped spacerand the one or more QWs of the p-type modulation doped QW structure1015. All of the layers grown thus far form the p-channel HFET devicewith the gate ohmic contact on the bottom. Deposited on the p-typemodulation doped QW structure 1015 is one or more spacer/barrier layers1017. Deposited on the spacer/barrier layer(s) 1017 is the QD-In-QWstructure 1019 (which corresponds to the p-type modulation doped QWstructure 1015). The spacer layer(s) 1021 is then formed on the QD-In-QWstructure 1019.

Deposited on the spacer layer(s) 1021 is the QD-In-QW structure 1023(which corresponds to the n-type modulation doped QW structure 1027)followed by one or more spacer layers(s) 1025. The n-type modulationdoped QW structure 1027 is formed on the spacer layer(s) 1025. Then-type modulation doped QW structure 1027 defines an n-type charge sheetoffset from one or more QWs by an undoped spacer layer. The n-typecharge sheet is formed last above the undoped spacer and the one or moreQWs of the n-type modulation doped QW structure 1027.

Deposited on the n-type modulation doped QW structure 1027 is one ormore spacer layer(s) 1029 and one or more p-type layers 1031, which canserve electrically as part of the gate of the n-channel HFET andoptically as part of the upper waveguide cladding of the device.Preferably, the p-type layers 1031 include two sheets of planar dopingof highly doped p-material separated by a lightly doped layer ofp-material. These p-type layers are offset from the n-type modulationdoped quantum well structure 1027 by the spacer layer(s) 1029. In thisconfiguration, the top charge sheet achieves low gate contact resistanceand the bottom charge sheet defines the capacitance of the n-channelHFET with respect to the n-type modulation doped QW structure 1027.Deposited on p-type layer(s) 1031 is one or more p-type ohmic contactlayer(s) 1033, which enables the formation of ohmic contacts thereto.Deposited on the p-type ohmic contact layer(s) 1033 is an optical guidelayer 1035.

The self-assembled quantum dots (QDs) embedded within the QD-in-QWstructures 1019 and 1023 improves the efficiency of the optoelectronicdevices realized from the active device structure of FIG. 10.Specifically, the population inversion necessary for laser action andamplification and the photon absorption mechanism for necessary foroptical detection occurs more efficiently with the introduction of thequantum dots and thus decreases the necessary current required forlasing action and amplification increases the photocurrent produced byabsorption. Furthermore, the size of the embedded QDs can be controlledto dictate the wavelength of the desired optical function (emission forlasing, amplification, absorption for detection). For example, the sizeof the QDs in either or both QD-in-QW structures 1019, 1023 can becontrolled to dictate the wavelength in range from 1300 nm up to 1550 nmfor use in the 0 to L (1260-1625 nm) bands employed in commercialoptical telecommunication networks.

Furthermore, the density distribution of the embedded QDs can becontrolled to dictate the laser output power. High density of embeddedQDs can provide for an increase of laser output power, but require agreater threshold lasing current.

The QD-in-QW structures 1019 and 1023 can be realized by first andsecond bilayer structures with an undoped barrier layer therebetween.Both the first and second bilayer structures include a templatesubstructure offset from an emission substructure by a thin undopedbarrier layer as described in detail in U.S. patent application Ser. No.13/921,311, which was filed on Jun. 19, 2013, hereinafter incorporatedby reference in its entirety.

The template substructures each include an un-graded QW withself-assembled QDs embedded therein. The self-assembled QDs can beformed during molecular beam epitaxy growth by a self-assembly methodknown as the Stranski-Krastanov process. In this process, an initiallayer (such as InGaAs) that is part an ungraded quantum well isdeposited. A compound semiconductor that is lattice mismatched relativeto the initial layer and underlying layer is deposited on the initiallayer. In particular, the lattice mismatch of the compound semiconductoris such that the growth forms three dimensional islands after adeposition of a critical thickness of the compound semiconductor. Thegrowth is continued to allow the three dimensional islands to expand toform the self-assembled QDs that have the desired characteristicdimensional range. After the self-assembled QDs are formed on theinitial layer, the deposition of the ungraded QW material resumes suchthat the self-assembled QDs are covered and fully embedded within theungraded QW material.

The emission substructures each include an analog-graded QW withself-assembled QDs embedded therein. The self-assembled QDs can beformed during molecular beam epitaxy growth by a self-assembly methodknown as the Stranski-Krastanov process similar to the growth conditionsof the template substructure. In this process, an initial layer (such asInGaAs) that is part an analog-graded quantum well is deposited. Acompound semiconductor that is lattice mismatched relative to theinitial layer and underlying layer is deposited on the initial layer. Inparticular, the lattice mismatch of the compound semiconductor is suchthat the growth forms three dimensional islands after a deposition of acritical thickness of the compound semiconductor. The three dimensionalislands of the emission substructure are formed such that they arealigned with the self-assembled QDs of the underlying templatestructure. The growth is continued to allow the three dimensionalislands to expand to form the self-assembled QDs that have the desiredcharacteristic dimensional range. After the self-assembled QDs areformed on the initial layer, the deposition of the analog-graded QWmaterial resumes such that the self-assembled QDs are covered and fullyembedded within the analog-graded QW of the respective emissionstructure.

The size of the QDs of the template and emission substructures candictate the wavelength of the electromagnetic radiation emitted orabsorbed for the desired optical function (laser emission,amplification, optical detection). For example, the size of the QDs ofthe template and emission substructures can be controlled to dictate theemission/absorption wavelength in range from 1300 nm up to 1550 nm foruse in the 0 to L (1260-1625 nm) bands employed in commercial opticaltelecommunication networks. Furthermore, the characteristicemission/absorption wavelengths can be different for QDs of the templateand emission substructures for the QD-in-QW structures 1019 and 1023,respectively. For example, the size of the QDs of the template andemission substructures for the QD-in-QW structure 1019 can be controlledto dictate the emission/absorption wavelength in range near 1310 nm, andthe size of the QDs of the template and emission substructures for theQD-in-QW structure 1023 can be controlled to dictate theemission/absorption wavelength in range near 1550 nm.

Furthermore, the density distribution of the QDs of the template andemission substructures dictates the laser output power. A high densityof embedded QDs can provide for an increase of laser output power, butrequire a greater threshold lasing current. The density distribution ofthe QDs of the template substructures dictates the density distributionof the QDs of the adjacent emission substructure and allows the growthconditions of the emission substructure to be tuned to control the sizeof the QDs of the adjacent emission substructure. Furthermore, thetemplate substructure relaxes the strain mismatch of the emissionsubstructure that arises from the layer underlying the templatesubstructure and thus allows for the larger sized QDs to be assembled inthe adjacent emission substructure.

FIGS. 11A-F, collectively, illustrate an exemplary layer structureutilizing group III-V materials for realizing the device structure ofFIG. 10 as described herein. The layer structure of FIGS. 11A-F can bemade, for example, using known molecular beam epitaxy (MBE) techniques.Starting from FIG. 11F, a semiconductor layer 1103 of aluminum arsenide(AlAs) and a semiconductor layer 1105 of gallium arsenide (GaAs) arealternately deposited (with preferably at least seven pairs) upon asemi-insulating GaAs substrate 1101 in sequence to form the bottom DBRmirror layers. The number of AlAs layers will preferably always be onegreater than the number of GaAs layers so that the first and last layersof the mirror are shown as layer 1103. In the preferred embodiment, theAlAs layers 1103 are subjected to high temperature steam oxidationduring fabrication to produce the compound Al_(x)O_(y) so that a mirrorwill be formed at the designed center wavelength. This center wavelengthis selected such that all of the desired resonant wavelengths for thedevice structures will be subject to high reflectivity. In oneembodiment, the thicknesses of layers 1103 and 1105 in the mirror can bechosen so that the final optical thickness of GaAs and Al_(x)O_(y) areone quarter wavelength of the center wavelength λ_(C). Alternatively themirrors could be grown as alternating layers of one-quarter wavelengththickness of GaAs and AlAs at the designed wavelength so that theoxidation step is not used. In that case, many more pairs are required(with typical numbers such as 27.5 pairs) to achieve the reflectivityneeded for efficient optical lasing and detection. The layers 1103 and1105 correspond to the bottom DBR mirror layers 1003 of FIG. 10 asdescribed above. The substrate 1101 corresponds to the substrate 1001 ofFIG. 10 as described above.

Deposited on the last bottom mirror layer 1103 is the metamorphic bufferthat significantly reduces strain due lattice mismatch between theoverlying active device structure of InGaAs material as described hereinand the underlying bottom DBR mirror layers and the GaAs substrate 1101.Specifically, the metamorphic buffer accommodates lattice mismatchbetween the underlying structure (bottom DBR mirror layers 1003 andsubstrate 1001) and the overlying structure (the alloys of the activedevice structure) and absorbs strain due to such lattice mismatch whileminimizing the nucleation of dislocations. The metamorphic buffer beginswith a buffer layer 1107 of undoped GaAs having a typical thickness of34 Å. A super-lattice 1109 of Al_(yl)Ga_((1-yl))As and GaAs arealternately deposited (with preferably at least five pairs) on thebuffer layer 1107. Al_(yl)Ga_((1-yl))As is an alloy of AlAs and GaAswhere the parameter yl is the proportion of AlAs and (1-yl) is theproportion of GaAs. The parameter yl is preferably at or near 50% (morepreferably at 52%) for the super-lattice 1109. The Al_(yl)Ga_((1-yl))Aslayers and the GaAs layers of the super-lattice 1109 have a typicalthickness of 2.4 Å and 1.4 Å, respectively. Next, a layer 1111 ofIn_(x1)Al_((1-x1))As is deposited on the super-lattice 1109.In_(x1)Al_((1-x1))As is an alloy of InAs and AlAs where the parameter x1is the proportion of InAs and (1-x1) is the proportion of AlAs. Theparameter x1 is preferably graded in an analog manner from 5% to 28% forlayer 1111. The In_(x1)Al_((1-x1))As layer 1111 has a typical thicknessof 340 Å. The grading is carried out in the growth direction for allgraded layers of FIGS. 11A-11F. The substrate temperature is controlledto a temperate preferably at or near 600° C. when depositing layers 1102to 1109. Next, an inverse step layer 1113 of In_(x1)Al_((1-x1))As isdeposited on layer 1111. The parameter x1 is preferably graded in ananalog manner from 28% to 25% for layer 1113 and thus layer 1113 matcheslayers 1111 at the interface between layers 1113 and 1111. TheIn_(x1)Al_((1-x1))As layer 1113 has a typical thickness of 20 Å. Thesubstrate temperature is controlled to a temperate preferably in therange of 400-450° C. when depositing layers 1111 to 1235 as describedherein. Next, a healing layer 1115 of In_(x1)Al_((1-x1))As is depositedon layer 1113. The parameter x1 is constant preferably at 25% for layer1115 and thus layer 1115 matches layer 1113 at the interface betweenlayers 1115 and 1113. The In_(x1)Al_((1-x1))As layer 1115 has a typicalthickness of 120 Å. Next, a layer 1117 of In_(x1)Al_((1-x1))As isdeposited on layer 1115. The parameter x1 is preferably graded in ananalog manner from 25% to 52% for layer 1117 and thus layer 1117 matcheslayer 1115 at the interface between layers 1117 and 1115. TheIn_(x1)Al_((1-x1))As layer 1117 has a typical thickness of 380 Å. Next,an inverse step layer 1119 of In_(x1)Al_((1-x1))As is deposited on layer1117. The parameter x1 is preferably graded in an analog manner from 52%to 49% for layer 1119 and thus layer 1119 matches layer 1117 at theinterface between layers 1119 and 1117. The In_(x1)Al_((1-x))As layer1119 has a typical thickness of 20 Å. Next, a healing layer 1121 ofIn_(x1)Al_((1-x1))As is deposited on layer 1119. The parameter x1 isconstant preferably at 49% for layer 1121 and thus layer 1121 matcheslayer 1119 at the interface between layers 1121 and 1119. TheIn_(x1)Al_((1-x1))As layer 1121 has a typical thickness of 110 Å. Notethat the inverse step and healing layers of the metamorphic bufferprovide a relatively abrupt change of strain in the respective inversestep layers and thus promotes isolated threading dislocations in theinverse step layers while reducing threading dislocations in the layersthereabove and thus provide smoother growing surfaces. The layers 1107to 1121 corresponds to the metamorphic buffer 1005 of FIG. 10 asdescribed above.

Deposited on layer 1121 is a spacer layer 1123 of undopedIn_(x1)Ga_((1-x1))As. In_(x1)Ga_((1-x1))As is an alloy of InAs and GaAswhere the parameter x1 is the proportion of InAs and (1-x1) is theproportion of GaAs. The parameter x1 is constant preferably at 53% forlayer 1123. The In_(x1)Ga_((1-x1))As layer 1123 has a typical thicknessof 200 Å. The In_(x1)Ga_((1-x1))As layer 1123 functions to eliminateanti-null absorption. The spacer layer 1123 corresponds to the spacerlayer 1007 of FIG. 10 as described above.

Deposited on spacer layer 1123 is the active device structure whichbegins with layer 1125 of N+ type In_(x1)Ga_((1-x1))As that enables theformation of ohmic contacts thereto. The parameter x1 is constantpreferably at 53% for layer 1125 and thus layer 1125 matches spacerlayer 1123. Layer 1125 has a typical thickness near 3000 Å and a typicaln-type doping of 3.5×10¹⁸ cm⁻³. The N+ doped In_(x1)Ga_((1-x1))As layer1125 corresponds to the bottom n-type ohmic contact layer 1009 of FIG.10 as described above.

Deposited on layer 1125 is layer 1127 of n-type In_(x1)Al_((1-x1))Aswith a typical thickness of 600-1000 Å and a typical doping of 5×10¹⁷cm⁻³. The parameter x1 is preferably 52% for layer 1127. The widebandmaterial of layer 1125 serves as part of the gate region of thep-channel HFET device and optically as a small part of the lowerwaveguide cladding of the respective optical device. Note that amajority of the lower waveguide cladding for waves propagating in theguide formed by the optically active region of the device is provided bythe lower DBR mirror itself. Next are four layers (1129, 1131, 1133,1135) comprising a stack of an alternating tertiary alloy of InGaAs anda quaternary alloy of InAlGaAs. These four layers collectively have atotal thickness of about 125 Å and doped N+ with a typical n-type dopingof 3.5×10¹⁸ cm⁻³. The first layer 1129 is a tertiary alloy ofIn_(x1)Ga_((1-x1))As where the parameter x1 is preferably 53% and with atypical thickness of 12 Å. The second layer 1131 is a quaternary alloyof In_(x1)Al_(x2)Ga_((1-x1-x2))As. In_(x1)Al₂Ga_((1-x1-x2))As is analloy of InAs, AlAs and GaAs where the parameter x1 is the proportion ofInAs, the parameter x2 is the proportion of AlAs and (1-x1-x2) is theproportion of GaAs. The parameters x1 and x2 for layer 1131 ispreferably 53% and 21%, respectively, and layer 1131 has a typicalthickness of 20 Å. The third layer 1133 is a tertiary alloy ofIn_(x1)Ga_((1-x1))As where the parameter x1 of layer 1133 is preferably53% and with a typical thickness of 12 Å. The fourth layer 1135 is aquaternary alloy of In_(x1)Al_(x2)Ga_((1-x1-x2))As where the parametersx1, x2 of layer 1135 are preferably 53% and 21%, respectively, and layer1135 has a typical thickness of 80 Å. The stack of layers 1129, 1131,1133, 1135 are mid-band gap materials and operate to trap defects fromthe Al material of layer 1131. The n-type layers 1127 to 1135 correspondto the bottom n-type layer(s) 1011 of FIG. 10.

Next is an undoped layer 1137 formed from a quaternary alloy ofIn_(x1)Al_(x2)Ga_((1-x1-x2))As, where the parameters x1 and x2 of layer1137 are preferably 53% and 21%, respectively. Layer 1137 has a typicalthickness of 300 Å. The undoped InAlGaAs layer 1137 corresponds to thespacer layer(s) 1013 of FIG. 10 as described above.

Next is a thin p-type charge sheet 1139 formed from a quaternary alloyof In_(x1)Al_(x2)Ga_((1-x1-x2))As, where the parameters x1 and x2 oflayer 1139 are preferably 53% and 21%, respectively. Layer 1139 is dopedP+ with a typical p-type doping of 7×10¹⁸ cm⁻³ and has a typicalthickness of 40 Å. Next is a undoped spacer layer 1141 formed from thequaternary alloy of In_(x1)Al_(x2)Ga_((1-x1-x2))As, where the parametersx1 and x2 of layer 1141 are preferably 53% and 21%, respectively. Layer1141 has a typical thickness of 30 Å. Next, an undoped InGaAs barrierlayer 1143 and an InGaAs quantum well layer 1145 are repeated for anumber of quantum wells (such as three or more quantum wells) for theinverted p-type modulation doped quantum structure. Single quantum wellstructures may also be used. The undoped InGaAs barrier layer 1143 isformed from a tertiary alloy of In_(x1)Ga_((1-x1))As, where theparameter x1 is preferably 53%. Layer 1143 has a typical thickness of 15Å. The InGaAs quantum well layer 1145 is formed from a tertiary alloy ofIn_(x1)Ga_((1-x1))As, where the parameter x1 is preferably 70%. Layer1145 has a typical thickness of 60 Å. Layers 1139 to 1145 correspond tothe inverted p-type modulation doped quantum structure 1015 of FIG. 10as described above.

An undoped InGaAs layer 1147 follows the last InGaAs quantum well layer.The undoped InGaAs layer 1147 is formed from a tertiary alloy ofIn_(x1)Ga_((1-x1))As, where the parameter x1 is preferably 53%. Layer1147 has a typical thickness of 300-500 Å. Layer 1147 corresponds tospacer layer 1017 of FIG. 10 as described above.

Following layer 1147 are layers 1149 to 1177 that correspond to theQD-in QW structure 1019 of FIG. 10 as described above. Layers 1149 to1153 form the template QD structure with InAs QDs embedded within anon-graded In_(x1)Ga_((1-x1))As quantum well where the parameter x1 is70%. The initial layer 1149 of the In_(x1)Ga_((1-x1))As quantum wellthat is deposited before the InAs QD growth sequence (specified as 1151)is preferably about 2 Å thick. The layer 1153 of theIn_(x1)Ga_((1-x1))As quantum well that is deposited after the InAs QDgrowth sequence is preferably about 40-60 Å thick. An undopedIn_(x1)Ga_((1-x1))As barrier layer 1155 is deposited on the InGaAsquantum well layer 1153. The parameter x1 of the undopedIn_(x1)Ga_((1-x1))As barrier layer 1155 is preferably 53%. Layer 1155has a typical thickness of 100 Å. Layers 1157 to 1161 form the emissionQD structure on the barrier layer 1155. The emission QD structureincludes InAs QDs embedded within an In_(x1)Ga_((1-x1))As quantum wellthat employs analog grading of In content. The initial layer 1157 of theIn_(x1)Ga_((1-x1))As quantum well that is deposited before the InAs QDgrowth sequence (specified as 1159) is preferably about 40 Å thick andhas analog grading of In content with the parameter x1 of 53% at theinterface to barrier layer 1155 to the parameter x1 of 70% at theinterface of the InAs QD growth sequence. The layer 1161 of theIn_(x1)Ga_((1-x1))As quantum well that is deposited after the InAs QDgrowth sequence (specified as 1159) is preferably about 40 Å thick andhas analog grading of In content with the parameter x1 of 70% at theinterface of the InAs QD growth sequence to the parameter x1 of 53% atthe interface to barrier layer 1163.

An undoped In_(x1)Ga_((1-x1))As barrier layer 1163 is deposited on thetop InGaAs quantum well layer 1161. The parameter x1 of the undopedIn_(x1)Ga_((1-x1))As barrier layer 1163 is preferably 53%. The undopedIn_(x1)Ga_((1-x1))As barrier layer 1163 is preferably about 300-500 Åthick.

Following barrier layer 1163 are layers 1165 to 1169 that form thetemplate QD structure with InAs QDs embedded within a non-gradedIn_(x1)Ga_((1-x1))As quantum well where the parameter x1 is 70%. Theinitial layer 1165 of the In_(x1)Ga_((1-x1))As quantum well that isdeposited before the InAs QD growth sequence (specified as 1167) ispreferably about 2 Å thick. The layer 1169 of the In_(x1)Ga_((1-x1))Asquantum well that is deposited after the InAs QD growth sequence ispreferably about 40-60 Å thick. An undoped In_(x1)Ga_((1-x1))As barrierlayer 1171 is deposited on the InGaAs quantum well layer 1169. Theparameter x1 of the undoped In_(x1)Ga_((1-x1))As barrier layer 1171 ispreferably 53%. Layer 1171 has a typical thickness of 100 Å. Layers 1173to 1177 form the emission QD structure on the barrier layer 1171. Theemission QD structure includes InAs QDs embedded within anIn_(x1)Ga_((1-x1))As quantum well that employs analog grading of Incontent. The initial layer 1173 of the In_(x1)Ga_((1-x1))As quantum wellthat is deposited before the InAs QD growth sequence (specified as 1175)is preferably about 40 Å thick and has analog grading of In content withthe parameter x1 of 53% at the interface to barrier layer 1175 to theparameter x1 of 70% at the interface of the InAs QD growth sequence. Thelayer 1177 of the In_(x1)Ga_((1-x1))As quantum well that is depositedafter the InAs QD growth sequence (specified as 1175) is preferablyabout 40 Å thick and has analog grading of In content from the parameterx1 of 70% at the interface of the InAs QD growth sequence to theparameter x1 of 53% at the interface to spacer layer 1179.

Next is an undoped spacer layer 1179 formed from a quaternary alloy ofIn_(x1)Al_(x2)Ga_((1-x1-x2))As, where the parameters x1 and x2 arepreferably 53% and 21%, respectively. Layer 1179 has a typical thicknessof 4000 Å. Layer 1179 correspond to the spacer layer(s) 1021 of FIG. 10as described above.

Following the spacer layer 1179 are layers 1181 to 1211 that correspondto the QD-in QW structure 1023 of FIG. 10 as described above. Layer 1181is an undoped In_(x1)Ga_((1-x1))As barrier layer preferably with theparameter x1 of 53% and with a thickness on the order of 300-500 Å.Layers 1183 to 1187 form the template QD structure with InAs QDsembedded within a non-graded In_(x1)Ga_((1-x1))As quantum well where theparameter x1 is 70%. The initial layer 1183 of the In_(x1)Ga_((1-x1))Asquantum well that is deposited before the InAs QD growth sequence(specified as 1185) is preferably about 2 Å thick. The layer 1187 of theIn_(x1)Ga_((1-x1))As quantum well that is deposited after the InAs QDgrowth sequence is preferably about 40-60 Å thick. An undopedIn_(x1)Ga_((1-x1))As barrier layer 1189 is deposited on the InGaAsquantum well layer 1153. The parameter x1 of the undopedIn_(x1)Ga_((1-x1))As InGaAs barrier layer 1189 is preferably 53%. Layer1189 has a typical thickness of 100 Å. Layers 1191 to 1195 form theemission QD structure on the barrier layer 1189. The emission QDstructure includes InAs QDs embedded within an In_(x1)Ga_((1-x1))Asquantum well that employs analog grading of In content. The initiallayer 1191 of the In_(x1)Ga_((1-x1))As quantum well that is depositedbefore the InAs QD growth sequence (specified as 1193) is preferablyabout 40 Å thick and has analog grading of In content with the parameterx1 of 53% at the interface to barrier layer 1189 to the parameter x1 of70% at the interface of the InAs QD growth sequence. The layer 1195 ofthe In_(x1)Ga_((1-x1))As quantum well that is deposited after the InAsQD growth sequence (specified as 1193) is preferably about 40 Å thickand has analog grading of In content from the parameter x1 of 70% at theinterface of the InAs QD growth sequence to the parameter x1 of 53% atthe interface to barrier layer 1197.

An undoped In_(x1)Ga_((1-x1))As barrier layer 1197 is deposited on thetop InGaAs quantum well layer 1195. The parameter x1 of the undopedIn_(x1)Ga_((1-x1))As barrier layer 1197 is preferably 53%. The undopedInGaAs barrier layer 1197 is preferably about 300-500 Å thick.

Following barrier layer 1197 are layers 1199 to 1203 that form thetemplate QD structure with InAs QDs embedded within a non-gradedIn_(x1)Ga_((1-x1))As quantum well with the parameter x1 of 70%. Theinitial layer 1199 of the In_(x1)Ga_((1-x1))As quantum well that isdeposited before the InAs QD growth sequence (specified as 1201) ispreferably about 2 Å thick. The layer 1203 of the In_(x1)Ga_((1-x1))Asquantum well that is deposited after the InAs QD growth sequence ispreferably about 40-60 Å thick. An undoped In_(x1)Ga_((1-x1))As barrierlayer 1205 is deposited on the InGaAs quantum well layer 1203. Theparameter x1 of the undoped In_(x1)Ga_((1-x1))As barrier layer 1205 ispreferably 53%. Layer 1205 has a typical thickness of 100 Å. Layers 1207to 1211 form the emission QD structure on the barrier layer 1205. Theemission QD structure includes InAs QDs embedded within anIn_(x1)Ga_((1-x1))As quantum well that employs analog grading of In.content The initial layer 1207 of the In_(x1)Ga_((1-x1))As quantum wellthat is deposited before the InAs QD growth sequence (specified as 1209)is preferably about 40 Å thick and has analog grading of In content withthe parameter x1 of 53% at the interface to barrier layer 1205 to theparameter x1 of 70% at the interface of the InAs QD growth sequence. Thelayer 1211 of the In_(x1)Ga_((1-x1))As quantum well that is depositedafter the InAs QD growth sequence (specified as 1209) is preferablyabout 40 Å thick and has analog grading of In content with the parameterx1 of 70% at the interface of the InAs QD growth sequence to theparameter x1 of 53% at the interface to barrier layer 1213.

An undoped In_(x1)Ga_((1-x1))As barrier layer 1213 is deposited on theInGaAs quantum well layer 1211. The parameter x1 of the undopedIn_(x1)Ga_((1-x1))As barrier layer 1213 is preferably 53%. Layer 1213has a typical thickness of 300-500 Å and corresponds to the spacer layer1025 of FIG. 10 as described above.

Next is an InGaAs quantum well layer 1215 and an undoped InGaAs barrierlayer 1217 that are repeated for a number of quantum wells (such asthree or more quantum wells) for the n-type modulation doped quantumstructure. Single quantum well structures may also be used. The InGaAsquantum well layer 1215 is formed from a tertiary alloy ofIn_(x1)Ga_((1-x1))As, where the parameter x1 is preferably 70%. Layer1215 has a typical thickness of 60 Å. The undoped InGaAs barrier layer1217 is formed from a tertiary alloy of In_(x1)Ga_((1-x1))As, where theparameter x1 is preferably 53%. Layer 1217 has a typical thickness of 15Å. Next is a undoped spacer layer 1219 formed from a quaternary alloy ofIn_(x1)Al_(x2)Ga_((1-x1-x2))As where the parameters x1 and x2 arepreferably 53% and 21%, respectively. Layer 1219 has a typical thicknessof 30 Å. Next is a thin n-type charge sheet 1221 formed from aquaternary alloy of In_(x1)Al_(x2)Ga_((1-x1-x2))As, where the parametersx1 and x2 are preferably 53% and 21%, respectively. Layer 1221 is dopedN+ with a typical n-type doping of 3.5×10¹⁸ cm⁻³ and has a typicalthickness of 80 Å. The layers 1215 to 1221 corresponds to the n-typemodulation doped quantum well structure 1027 of FIG. 10 as describedabove.

Next is an undoped layer 1223 formed from a quaternary alloy ofIn_(x1)Al_(x2)Ga_((1-x1-x2))As, where the parameters x1 and x2 arepreferably 53% and 21%, respectively. Layer 11223 has a typicalthickness of 300 Å. The undoped InAlGaAs layer 1223 corresponds to thespacer layer(s) 1029 of FIG. 10 as described above.

Next are three layers (1225, 1227, 1229) that have a total thickness ofabout 700-800 Å and are doped with p-type doping. The first layer 1225is a quaternary alloy of In_(x1)Al_(x2)Ga_((1-x1-x2))As where theparameters x1 and x2 are preferably 53% and 21%, respectively. The firstlayer 1225 is P+ doped with a typical p-type doping of 7×10¹⁸ cm⁻³ andhas a typical thickness of 60 Å. The second layer 1227 is a tertiaryalloy of In_(x1)Ga_((1-x1))As where the parameter x1 is preferably 53%.The second layer 1227 is P+ doped with a typical p-type doping of 7×10¹⁸cm⁻³ and has a typical thickness of 12 Å. The third layer 1229 is atertiary alloy of In_(x1)Al_((1-x1))As where the parameter x1 ispreferably 52%. The third layer 1229 is P doped with a typical p-typedoping of 5×10¹⁷ cm⁻³ and has a typical thickness of 700 Å. The widebandmaterial of layer 1229 serves as part of the gate region of then-channel HFET device and optically as upper waveguide cladding of therespective optical device. The n-type layers 1225 to 1229 correspond tothe top n-type layer(s) 1031 of FIG. 10 as described above.

Next is layers 1231 and 1233 of P+ type In_(x1)Ga_((1-x1))As thatenables the formation of ohmic contacts thereto. The parameter x1 oflayers 1231 and 1233 is constant preferably at 53%. Layer 1231 has atypical thickness near 900 Å and a typical p-type doping of 7×10¹⁸ cm⁻³.Layer 1233 has a typical thickness near 60 Å and a typical p-type dopingof 1×10²⁰ cm⁻³. The P+ doped In_(x1)Ga_((1-x1))As layers 1231 and 1233corresponds to the top p-type ohmic contact layer(s) 1133 of FIG. 10 asdescribed above.

Deposited on layer 1233 is layer 1235 of undoped In_(x1)Ga_((1-x1))Aswith a typical thickness of 700-1000 Å (more preferably near 870 Å). Theparameter x1 for layer 1233 is preferably 53%. Layer 1235 can be used toform an aperture for optical devices (such as VCSELs) as describedherein and to form active and passive in-plane optical waveguidestructures (such as the active and passive sections of the closed-pathwaveguides) as described herein. Layer 1233 corresponds to the opticalguide layer 1035 of FIG. 10 as described above.

Note that the size of the embedded QDs of the template and emissionsubstructures of the template and emission QD substructures contributesto the emission/absorption wavelength of such structures. In oneembodiment, the embedded QDs of the template and emission substructureshave the following characteristics:

-   -   QDs of the emission substructure having a maximal characteristic        dimension of 50-60 Å for production/absorption of light with a        characteristic wavelength at or near 1310 nm, and QDs of the        template substructure having a maximal characteristic dimension        of 20-30 Å (which are of smaller size that the emission        substructure) for production/absorption of light with a        characteristic wavelength at or near 1310 nm;    -   QDs of the emission substructure having maximal characteristic        dimension of 20-30 Å for production/absorption of light with a        characteristic wavelength at or near 1430 nm, and QDs of the        template substructure having a maximal characteristic dimension        of 20-30 Å (which are of smaller size that the emission        substructure) for production/absorption of light with a        characteristic wavelength at or near 1430 nm;    -   QDs of the emission substructure having a maximal characteristic        dimension of 100-110 Å for production/absorption of light with a        characteristic wavelength at or near 1550 nm, and QDs of the        template substructure having a maximal characteristic dimension        of 20-30 Å (which are of smaller size that the emission        substructure) for production/absorption of light with a        characteristic wavelength at or near 515 nm; and    -   QDs with an aspect ratio on the order of three (i.e., the        characteristic base dimension of the QD is about three times        larger than the characteristic height dimension of the QD).        Such QD size and aspect ratio are dictated by growth conditions,        particularly the number of monolayers for three dimensional InAs        QD growth. For example, 2 ML of three dimensional InAs QD growth        can be used for the template substructures, and 3.2 ML of three        dimensional InAs QD growth can be used for the emission        substructures. Other suitable monolayer growths can be used as        well. Moreover, the thickness of the barrier layer(s) between        the QDs of the template substructure and the emission        substructure can be controlled in order that the strain energy        from the template substructure have a desired influence on the        larger dot size and quality of the emission substructure.        Moreover, the In concentration of the analog graded quantum well        material onto which the QDs are grown can be used to control the        amount of strain and thus the maximum size of the QDs formed        thereon. For example, the analog graded quantum well layers of        the emission substructures can have a maximum relative        concentration of In greater than 70% (for example up to or        beyond 90%) in order to reduce the amount of strain and thus        increase the maximum size of the QDs formed thereon.

Also note the incorporation of In into the quantum wells of the n-typeand p-type modulation doped quantum well structures can greatly improvethe frequency response (i.e., higher cutoff frequencies) for transistordevices including the n-channel HFET and the p-channel HFET devices.

FIGS. 12A to 12I illustrate exemplary fabrication steps that form anoptical feature (such as an aperture) this is aligned to patterned metaland one more underlying implant regions as part of optoelectronic devicerealized in an integrated circuit that employs the layer structure ofFIG. 10. The optical feature is formed at the top surface of the layerstructure of FIG. 10. The optical feature can be an aperture that allowsfor light to exit or enter into the active region of the device. Thepatterned metal regions and one or more underlying implant regions canbe used to block light from exiting or entering into the active regionof the device structure and thus form the boundary of the aperture.Similar methodology can also be used to form a passive and/or activein-plane waveguide structures as part of optoelectronic device realizedin an integrated circuit that employs the layer structure of FIG. 10.Such in-plane waveguide guides the propagation of light in the plane ofthe integrated circuit, and the optical feature formed at the topsurface provides for vertical confinement and wave guiding of light forthe top portion of the integrated circuit wafer. For the passivein-plane waveguide structure, the patterned metal can be omitted.

In the steps of FIGS. 12A to 12I, a protective layer 1201 (preferablyformed from silicon nitride) is deposited on the top surface of layer1035 of FIG. 10 as shown in FIGS. 12A and 12B. A mask (preferably formedfrom photoresist material) is deposited and patterned to define a maskfeature 1203 as shown in FIG. 12C. The mask feature 1203 protects thearea of the aperture 1205 that results from the process as shown in FIG.12I.

Then, mask feature 1203 is used as part of an etch operation that etchesthrough the exposed protective layer 1201 and underlying guide layer1035 to a depth at or near the top surface 1209 of layer 1033, and thusleaving behind a post that includes the protective layer 1201 andunderlying guide layer 1035 as shown in FIG. 12D. The post can includeone or more sidewalls (such as the two opposed sidewalls 1207A, 1207B)that extend through the protective layer 1201 and underlying guide layer1035 as shown. This etch operation can employ an anisotropic etchingprocess that define a near vertical profile for the sidewall(s) of thepost. An example of a suitable anisotropic etching process is dryreactive ion etching employing SF6.

Then, one or more implant regions such as two implant regions 1211A,1211B) are implanted through the top surface 1209 into the layerstructure outside the post as shown in FIG. 12E. In one embodiment, theone or more implant regions (e.g., regions 1211A, 1211B) are implantedto a depth that encompasses the top p-type layers 1031 of the layerstructure of FIG. 10. In this case, the one or more implant regions(e.g., implant regions 1211A, 1211B) employ n-type species of sufficientdensity that convert the p-type implanted region to n-type and produce apn junction that blocks the flow of hole current flow verticallydownwards. This forces the hole current to flow laterally to anun-implanted active region of the device structure disposed below thepost. In another, embodiment, the one or more implant regions (e.g.,regions 1211A and 1211B) can be implanted to a depth below the QW(s) ofthe n-type modulation doped QW structure 1027. This requires higherenergy to place the implant region(s) below such QW(s). In this case,the one or more implant regions (e.g., regions 1211A, 1211B) operate toincrease the “as grown” barrier to conduction of holes by the additionof more n type doping near the modulation doping of the n-typemodulation doped QW structure 1027. The larger barrier means that p-typeconduction over this barrier is reduced and so the hole current from thetop contact flows laterally where the barrier is lower (i.e., thevertically down conduction is blocked) preferentially to theun-implanted active region of the device structure disposed below thepost. The ions species of the implant region(s) can be Si ions due toits lower mass and larger possible range. SiF ions may also be used. Theadvantage of locating the current blocking implant region(s) below theQW of the n-type modulation doped QW structure 1027 is that the topp-type layers 1031 can be made thinner (preferably a ½λ above the QW),which makes it easier to fabricate HFETs with a lower profile topology.Another advantage of this approach is a lower laser resistance andtherefore reduced heat generation in the laser active region which isimportant for stable laser operation in the integrated environment. Theimplant region(s) (e.g., regions 211A, 1211B) can also provide forlateral confinement of light within the active region of the devicestructure disposed below the post.

Next, the protective layer 1201 of the post is removed and then metalmaterial 1213 for the top surface electrode, which can be tungsten orsome other suitable metal or metal alloy, is deposited and patternedsuch that it covers the top surface 1209 of layer 1033 and the topsurface and sidewalls of the guide layer 1035 of the post as evidentfrom FIG. 12F.

Next, a second mask layer 1215 (preferably formed from photoresistmaterial) is deposited and patterned to define a window 1216 thatoverlies the metal feature 1213 and the guide layer 1035 of the post asshown in FIG. 12G. The window 1216 is used as part of an etch operationthat etches down through the metal 1213 to a depth at or near the topsurface of the guide layer 1035 in the area that results in the aperture1205. This etch operation can employ a BOE (Buffered Oxide Etch) thatetches sideways and removes the top section of the exposed metal feature1213 to form the resultant structure as shown in FIG. 12H. The secondmask layer 1215 is then removed to form the structure as shown in 12Iwhere the aperture 1205 is formed between the opposed surface electrodeparts 1217A, 1217B.

Note that the current blocking implant region(s) (e.g., implant regions1211A, 1211B) are disposed on opposite sides of the aperture 1205 belowthe corresponding surface electrode parts 1217A, 1217B. Specifically,the opposed edges of the implant regions 1211A, 1211B are generallyaligned laterally with the opposed edges of the surface electrode parts1217A, 1217B that define the boundaries of the aperture 1215. Thisself-aligned configuration of the implant region(s) and the surfaceelectrode is advantageous because it can eliminate fabrication steps,aid in minimizing resistance of the top surface layers and aid inproducing uniformity and higher yield over large areas.

In alternate embodiments, similar methodology can be used to form apassive and/or active in-plane waveguide structures as part ofoptoelectronic device realized in an integrated circuit that employs thelayer structure of FIG. 10. Such in-plane waveguide guides thepropagation of light in the plane of the integrated circuit, and thewaveguide layer of the post feature formed at the top surface providesfor wave guiding of the in-plane propagating light at the top portion ofthe integrated circuit wafer. For the passive in-plane waveguidestructure, the patterned metal can be omitted.

In other alternate embodiments, the surface electrode that defines theboundaries of the aperture 1205 can be patterned and etched away aftermetallizing all of the electrodes of the devices of the integratedcircuit and prior to depositing the dielectric material of the topmirror of such device, if used.

There have been described and illustrated herein several embodiments ofan optoelectronic integrated circuit employing complementary modulationdoped quantum well structures and methods of fabricating the same. Whileparticular embodiments of the invention have been described, it is notintended that the invention be limited thereto, as it is intended thatthe invention be as broad in scope as the art will allow and that thespecification be read likewise. Thus, while particular group III-Vmaterial system and heterostructures have been disclosed, it will beappreciated that other III-V material systems and heterostructures canbe used to realize the optoelectronic integrated circuitry as describedherein. It will therefore be appreciated by those skilled in the artthat yet other modifications could be made to the provided inventionwithout deviating from its spirit and scope as claimed.

What is claimed is:
 1. A semiconductor device comprising: an epitaxiallayer arrangement including a first ohmic contact layer and firstmodulation doped quantum well structure disposed above the first ohmiccontact layer, wherein the first ohmic contact layer has a first dopingtype and the first modulation doped quantum well structure has amodulation doped layer of a second doping type; and at least one ionfirst-type implant region that extends above the first ohmic contactlayer.
 2. A semiconductor device according to claim 1, wherein: the atleast first-type one ion implant region comprises oxygen ions.
 3. Asemiconductor device according to claim 1, wherein: the at least onefirst-type ion implant region is substantially free of charge carriersin order to reduce a characteristic capacitance of the device.
 4. Asemiconductor device according to claim 1, wherein: the epitaxial layerarrangement further comprises at least one spacer layer disposed abovethe first modulation doped quantum well structure; the semiconductordevice further includes a mesa formed in the at least one spacer layer,at least one second-type ion implant region disposed below the mesa incontact with the first modulation doped quantum well structure, and atleast one electrode terminal formed on the mesa in contact with the atleast one second-type ion implant region; and the at least onefirst-type ion implant region is disposed below the mesa and below theat least one second-type ion implant region.
 5. A semiconductor deviceaccording to claim 1, wherein: the first modulation doped quantum wellstructure defines a QW channel of an HFET device, wherein the QW channelextends between opposed second-type ion implant regions that are incontact with corresponding source and drain terminal electrodes of theHFET device, and a gate terminal electrode of the HFET device is incontact with the first ohmic contact layer.
 6. A semiconductor deviceaccording to claim 1, wherein: the first modulation doped quantum wellstructure defines a QW channel of a BICFET device, wherein the QWchannel is in contact with a base terminal electrode of the BICFETdevice, and an emitter terminal electrode of the BICFET device is incontact with the first ohmic contact layer.
 7. A semiconductor deviceaccording to claim 1, wherein: the at least one first-type ion implantregion provides for lateral confinement of light within a resonantcavity defined by the epitaxial layer arrangement.
 8. A semiconductordevice according to claim 1, wherein: the first modulation doped quantumwell structure, the first ohmic contact layer and the at least onefirst-type ion implant region are all part of an optical resonatorformed in the epitaxial layer arrangement, wherein the optical resonatoris adapted to process light at at least one predetermined wavelength. 9.A semiconductor device according to claim 8, wherein: the opticalresonator includes a resonant cavity supporting propagation of anoptical signal therein, wherein the at least one first-type ion implantregion is disposed adjacent the resonant cavity.
 10. A semiconductordevice according to claim 9, further comprising: a first terminalelectrode in electrical contact with the first modulation doped quantumwell structure; and a second terminal electrode in electrical contactwith the first ohmic contact layer.
 11. A semiconductor device accordingto claim 10, wherein: the first and second terminal electrodes areconfigured as terminals of a diode laser whereby injected electricalcurrent flows between the first and second terminal electrodes andcauses light generation and propagation within the resonant cavity. 12.A semiconductor device according to claim 10, wherein: the first andsecond terminal electrodes are configured as terminals of a diodeoptical detector that carry electrical current caused by absorption oflight propagating within the resonant cavity.
 13. A semiconductor deviceaccording to claim 9, wherein: the epitaxial layer arrangement furthercomprises at least one spacer layer disposed above the first modulationdoped quantum well structure, a second modulation doped quantum wellstructure disposed above the at least one spacer layer, and a secondohmic contact layer disposed above the second modulation doped quantumwell structure, wherein the second modulation doped quantum wellstructure has a modulation doped layer of the first doping type and thesecond ohmic contact layer has the second doping type; and thesemiconductor device further includes a top terminal electrode inelectrical contact with the second ohmic contact layer, a first injectorterminal electrode in electrical contact with the second modulationdoped quantum well structure, a second injector terminal electrode inelectrical contact with the first modulation doped quantum wellstructure, and a bottom terminal electrode in electrical contact withthe first ohmic contact layer.
 14. A semiconductor device according toclaim 13, wherein: the top terminal electrode, the first injectorterminal electrode, the second injector terminal electrode, and thebottom terminal electrode are configured as terminals of a switchingthyristor laser having an ON state whereby current flows between the topterminal electrode and bottom terminal electrode to cause lightgeneration and propagation within the resonant cavity.
 15. Asemiconductor device according to claim 13, wherein: the top terminalelectrode, the first injector terminal electrode, the second injectorterminal electrode, and the bottom terminal electrode are configured asterminals of a switching thyristor optical detector having an ON statewhereby current flows between the top terminal electrode and bottomterminal electrode, wherein the ON state is caused by absorption oflight propagation in the resonant cavity.
 16. A semiconductor deviceaccording to claim 13, wherein: the optical resonator includes a firstvertical resonant cavity surrounded by an annular second resonant cavityformed in the epitaxial layer arrangement, wherein the at least onefirst-type ion implant region is disposed adjacent the second resonantcavity; the semiconductor device further includes a coupling waveguidestructure spaced from the second resonant cavity of optical resonator toprovide for evanescent-wave optical coupling therebetween; and theoptical resonator and the coupling waveguide structure are configured toperform predetermined optical mode transformation operations selectedfrom the group consisting of vertical propagation to in-planepropagation, in-plane propagation to vertical propagation, wavelengthconversion, and combinations thereof.
 17. A semiconductor deviceaccording to claim 9, wherein: the resonant cavity has a disk-like shapeand the optical signal comprises a whispering gallery optical signal, orthe resonant cavity has an annular-shape and the optical signalcomprises a circulating optical signal.
 18. A semiconductor deviceaccording to claim 9, wherein: the at least one first-type ion implantregion is disposed in a central region of the resonant cavity.
 19. Asemiconductor device according to claim 9, wherein: the opticalresonator includes a resonant cavity defined by a rib waveguide, whereinthe at least one first-type ion implant region is disposed on at leastone side of the rib waveguide.
 20. A semiconductor device according toclaim 19, wherein: the at least one first-type ion implant regionsincludes two first-type ion implant regions disposed on opposed sides ofthe rib waveguide.
 21. A semiconductor device according to claim 19,wherein: the rib waveguide has a plurality of straight sections that areoptically coupled together by bend sections.
 22. A semiconductor deviceaccording to claim 9, further comprising: a coupling waveguide structurespaced from the resonant cavity of optical resonator to provide forevanescent-wave optical coupling therebetween, wherein the resonantcavity of the optical resonator and coupling waveguide structure aredefined by sidewalls of the epitaxial layer arrangement.
 23. Asemiconductor device according to claim 22, wherein: the epitaxial layerarrangement is disposed above a bottom distributed Bragg reflector (DBR)mirror, wherein the sidewalls that define the resonant cavity of theoptical resonator and the coupling waveguide structure extend downwardto the bottom DBR mirror.
 24. A semiconductor device according to claim1, further comprising: a plurality of DBR mirror layers formed belowfirst ohmic contact layer of the epitaxial layer arrangement.
 25. Asemiconductor device according to claim 24, further comprising: aplurality of dielectric mirror layers formed above the epitaxial layerarrangement.
 26. A semiconductor device according to claim 1, wherein:said epitaxial layer arrangement includes an N+ type doped layer for thefirst ohmic contact layer, a first plurality of layers that define ap-type modulation doped quantum well structure for the first modulationdoped quantum well structure, a second plurality of layers that definean n-type modulation doped quantum well structure for the second n-typemodulation doped structure, and at least one P+ type doped layer for thesecond ohmic contact layer.
 27. A semiconductor device comprising: anoptical resonator including a first vertical resonant cavity surroundedby an annular second resonant cavity formed in an epitaxial layerarrangement; and a coupling waveguide structure spaced from the secondresonant cavity of optical resonator to provide for evanescent-waveoptical coupling therebetween.
 28. A semiconductor device according toclaim 27, wherein: the second resonant cavity of the optical resonatorand the coupling waveguide structure are defined by sidewalls of theepitaxial layer arrangement.
 29. A semiconductor device according toclaim 27, wherein: the coupling waveguide structure and the opticalresonator are configured to perform predetermined mode transformationoperations selected from the group consisting of vertical propagation toin-plane propagation, in-plane propagation to vertical propagation,wavelength conversion, and combinations thereof.
 30. A semiconductordevice according to claim 27, wherein: the epitaxial layer arrangementincludes a first ohmic contact layer, a first modulation doped quantumwell structure disposed above the first ohmic contact layer, at leastone spacer layer disposed above the first modulation doped quantum wellstructure, a second modulation doped quantum well structure disposedabove the spacer layer, and a second ohmic contact layer disposed abovethe second modulation doped quantum well structure; wherein the firstohmic contact layer has a first doping type, the first modulation dopedquantum well structure has a modulation doped layer of a second dopingtype, the second modulation doped quantum well structure has amodulation doped layer of the first doping type, and the second ohmiccontact layer has the second doping type.
 31. A semiconductor deviceaccording to claim 30, wherein the resonator further comprises: a topterminal electrode in electrical contact with the second ohmic contactlayer; at least one of a first injector terminal electrode and a secondinjector terminal, wherein the first injector terminal is in electricalcontact with the second modulation doped quantum well structure, and thesecond injector terminal electrode in electrical contact with the firstmodulation doped quantum well structure; and a bottom terminal electrodein electrical contact with the first ohmic contact layer.
 32. Asemiconductor device according to claim 31, wherein: the electrodes ofthe device are configured as terminals of a switching thyristor laserhaving an ON state, whereby current flows between the top terminalelectrode and bottom terminal electrode to cause light generation andpropagation within the vertical resonant cavity.
 33. A semiconductordevice according to claim 31, wherein: the electrodes of the device areconfigured as terminals of a switching thyristor optical detector havingan ON state whereby current flows between the top terminal electrode andbottom terminal electrode, wherein the ON state is caused by absorptionof light propagating in the vertical resonant cavity.
 34. Asemiconductor device comprising: an optical resonator including a closedpath waveguide that supports circulating propagation of light; awaveguide structure that is spaced from the closed path waveguide of theoptical resonator to provide for evanescent-wave optical couplingtherebetween; wherein the closed path waveguide includes at least oneactive section and a tuning section that is spaced from the at least oneactive section, wherein the active section is configured to generate orabsorb light that circulates in the closed path waveguide, and whereinthe tuning section is configured to provide electrical control of thewavelength of the light circulating in the closed path waveguide.
 35. Asemiconductor device according to claim 34, wherein: the closed pathwaveguide of the optical resonator and the waveguide structure are bothformed in an epitaxial layer structure that includes at least onemodulation doped quantum well structure with one or more quantum wells;and the tuning section of the closed path waveguide includes a pluralityof electrodes for supplying electrical signals that control charge inthe one or more quantum wells of the at least one modulation dopedquantum well structure of the epitaxial layer structure of the tuningsection in order to control the wavelength of the light circulating inthe closed path waveguide.
 36. A semiconductor device according to claim35, wherein the tuning section of the closed path waveguide is isolatedfrom the at least one active section by passive waveguide sections. 37.A semiconductor device comprising: an optical resonator including aclosed path waveguide that supports circulating propagation of light; awaveguide structure that is spaced from the closed path waveguide of theoptical resonator to provide for evanescent-wave optical couplingtherebetween, wherein the waveguide structure has one end disposedopposite an output end; and a reflector structure integral to said oneend of the waveguide structure, wherein the reflector structure includesa Bragg-grating.
 38. A semiconductor device according to claim 37,wherein: the reflector structure includes two co-planar radio-frequency(RF) traveling wave transmission lines disposed on opposite sides of theBragg-grating along the length of the Bragg-grating.
 39. A semiconductordevice according to claim 38, further comprising: a signal source thatsupplies a traveling wave RF signal to the two co-planar RF travelingwave transmission lines in order to selectively control the wavelengthof light that is reflected by the Bragg-grating of the reflectorstructure.
 40. A semiconductor device according to claim 37, wherein:the closed path waveguide of the optical resonator and the waveguidestructure and the reflector structure are all formed in an epitaxiallayer structure that includes at least one layer disposed above amodulation doped quantum well structure; and the Bragg-grating is formedin the at least one layer disposed above the modulation doped quantumwell structure.
 41. A method of forming a patterned layer of metal thatdefines an aperture of an optoelectronic device realized in anintegrated circuit wafer, the method comprising: depositing andpatterning a first mask on a top surface of the wafer, wherein thepattern of the first mask defines a mask feature that protects an areaof the aperture; performing an ion implant operation that forms at leastone ion implant region disposed adjacent the aperture; depositing metalsuch that the metal covers the top surface and the mask feature;depositing and patterning a second mask to define a window that overliesthe mask feature, wherein the window has a smaller width than width ofthe mask feature. performing a first etch operation that etches throughthe window defined by the second mask to a depth at or near the topsurface, where the first etch operation leaves behind at least onesidewall of the mask feature; and performing a second etch operationthat etches sideways and undercuts the at least one sidewall of the maskfeature as well as at least one adjacent sidewall of the metal to formthe aperture.
 42. A method according to claim 41, wherein: the firstmask comprises a dual layer structure of oxide and nitride.
 43. A methodaccording to claim 41, wherein: the at least one ion implant regionprovide for current funneling toward an active region under the apertureand/or lateral confinement of light within the active region under theaperture.
 44. A method according to claim 41, wherein: the metalcomprises tungsten; and/or the at least one sidewall of the mask featurethat results from the first etch operation has a width dimension on theorder of 1-2 μm; and/or the first etch operation employs an anisotropicetching process that defines a near vertical profile for the at leastone sidewall of the mask feature; and/or the second etch operationemploys a buffer-oxide etchant.
 45. An optoelectronic semiconductordevice comprising: a substrate; an epitaxial layer arrangement formed onthe substrate, wherein in the epitaxial layer arrangement includes abuffer structure and an active device structure formed on the bufferstructure; wherein the active device structure includes at least onemodulation doped quantum well structure spaced from a QD-in-QWstructure; and wherein the buffer structure comprises a plurality oflayer that are configured to accommodate lattice strain due to mismatchbetween the active device structure and the substrate.
 46. Anoptoelectronic semiconductor device according to claim 45, wherein: thesubstrate comprises a GaAs substrate; the at least one modulation dopedquantum well structure comprises at least one InGaAs quantum well formedfrom an alloy of InAs and GaAs that includes at least 70 percent InAs;and the QD-in-QW structure comprises quantum dots formed from InAs andembedded within at least one InGaAs quantum well formed from an alloy ofInAs and GaAs that includes at least 70 percent InAs.
 47. Anoptoelectronic semiconductor device according to claim 46, wherein: atleast one InGaAs quantum well of the QD-in-QW structure includes atemplate substructure formed below an emission substructure, wherein thetemplate substructure includes a non-graded InGaAs quantum well formedfrom an alloy of InAs and GaAs that includes less than 70 percent InAs,and wherein the emission substructure includes a graded InGaAs quantumwell formed from an alloy of InAs and GaAs that has a maximum percentageof InAs of at least 70 percent InAs.
 48. An optoelectronic semiconductordevice according to claim 46, wherein: the buffer structure comprises aplurality of layers formed from an alloy of InAs and AlAs.
 49. Anoptoelectronic semiconductor device according to claim 48, wherein: thebuffer structure further comprises a periodic superlattice layerstructure comprising a first layer formed from an alloy of AlAs and GaAsand a second layer formed from GaAs.
 50. A method of fabricating anoptoelectronic device realized in an integrated circuit wafer thatincludes a top layer overlying a doped ohmic contact layer andsemiconductor layers therebelow, the method comprising: depositing aprotective layer on the top layer; depositing and patterning a firstmask on the protective layer, wherein the pattern of the first maskprotects an area for an optical feature; performing a first etchoperation that etches down to the doped ohmic contact layer in order todefine the optical feature that includes the top layer, wherein thefirst etch operation exposes the doped ohmic contact layer adjacent atleast one side of the optical feature and leaves behind at least onesidewall of the optical feature; performing an ion implant operationthat forms at least one ion implant region in the semiconductor layersdisposed below the exposed doped ohmic contact layer adjacent the atleast one side of the optical feature; depositing and patterning asecond mask to define a window that overlies the optical feature; andperforming a second etch operation that uses the window of the secondmask to expose the top layer of the optical feature.
 51. A methodaccording to claim 50, wherein: the optical feature is selected fromgroup consisting of an aperture, a waveguide layer of an activewaveguide structure, and a waveguide layer of a passive waveguidestructure.
 52. A method according to claim 50, further comprising:depositing metal such that the metal covers the optical feature; whereinthe second mask is deposited on the metal and the window defined by thesecond mask exposes metal that covers the optical feature; and whereinthe second etch operation removes the metal that covers the opticalfeature in order to expose the top layer of the optical feature.
 53. Amethod according to claim 50, wherein: the top layer comprises anundoped semiconductor layer; and/or the protective layer comprises asilicon nitride layer; and/or the first etch operation employs ananisotropic etching process that define a near vertical profile for theat least one sidewall of the optical feature; and/or the second etchoperation employs a buffer-oxide etchant; and/or the at least one ionimplant region provides for current funneling toward an active regionunder the optical feature and/or lateral confinement of light in theactive region under the optical feature.